// SPDX-License-Identifier: GPL-2.0
#include <linux/anon_inodes.h>
#include <linux/exportfs.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/cgroup.h>
#include <linux/magic.h>
#include <linux/mount.h>
#include <linux/pid.h>
#include <linux/pidfs.h>
#include <linux/pid_namespace.h>
#include <linux/poll.h>
#include <linux/proc_fs.h>
#include <linux/proc_ns.h>
#include <linux/pseudo_fs.h>
#include <linux/ptrace.h>
#include <linux/seq_file.h>
#include <uapi/linux/pidfd.h>
#include <linux/ipc_namespace.h>
#include <linux/time_namespace.h>
#include <linux/utsname.h>
#include <net/net_namespace.h>
#include <linux/coredump.h>
#include <linux/rhashtable.h>
#include <linux/xattr.h>
#include <linux/cookie.h>

#include "internal.h"
#include "mount.h"

#define PIDFS_PID_DEAD ERR_PTR(-ESRCH)

static struct kmem_cache *pidfs_attr_cachep __ro_after_init;
static struct kmem_cache *pidfs_xattr_cachep __ro_after_init;

static struct path pidfs_root_path = {};

void pidfs_get_root(struct path *path)
{
        *path = pidfs_root_path;
        path_get(path);
}

enum pidfs_attr_mask_bits {
        PIDFS_ATTR_BIT_EXIT     = 0,
        PIDFS_ATTR_BIT_COREDUMP = 1,
};

struct pidfs_attr {
        unsigned long attr_mask;
        struct simple_xattrs *xattrs;
        struct /* exit info */ {
                __u64 cgroupid;
                __s32 exit_code;
        };
        __u32 coredump_mask;
        __u32 coredump_signal;
};

static struct rhashtable pidfs_ino_ht;

static const struct rhashtable_params pidfs_ino_ht_params = {
        .key_offset             = offsetof(struct pid, ino),
        .key_len                = sizeof(u64),
        .head_offset            = offsetof(struct pid, pidfs_hash),
        .automatic_shrinking    = true,
};

/*
 * inode number handling
 *
 * On 64 bit nothing special happens. The 64bit number assigned
 * to struct pid is the inode number.
 *
 * On 32 bit the 64 bit number assigned to struct pid is split
 * into two 32 bit numbers. The lower 32 bits are used as the
 * inode number and the upper 32 bits are used as the inode
 * generation number.
 *
 * On 32 bit pidfs_ino() will return the lower 32 bit. When
 * pidfs_ino() returns zero a wrap around happened. When a
 * wraparound happens the 64 bit number will be incremented by 1
 * so inode numbering starts at 1 again.
 *
 * On 64 bit comparing two pidfds is as simple as comparing
 * inode numbers.
 *
 * When a wraparound happens on 32 bit multiple pidfds with the
 * same inode number are likely to exist (This isn't a problem
 * since before pidfs pidfds used the anonymous inode meaning
 * all pidfds had the same inode number.). Userspace can
 * reconstruct the 64 bit identifier by retrieving both the
 * inode number and the inode generation number to compare or
 * use file handles.
 */

#if BITS_PER_LONG == 32

DEFINE_SPINLOCK(pidfs_ino_lock);
static u64 pidfs_ino_nr = 1;

static inline unsigned long pidfs_ino(u64 ino)
{
        return lower_32_bits(ino);
}

/* On 32 bit the generation number are the upper 32 bits. */
static inline u32 pidfs_gen(u64 ino)
{
        return upper_32_bits(ino);
}

static inline u64 pidfs_alloc_ino(void)
{
        u64 ino;

        spin_lock(&pidfs_ino_lock);
        if (pidfs_ino(pidfs_ino_nr) == 0)
                pidfs_ino_nr++;
        ino = pidfs_ino_nr++;
        spin_unlock(&pidfs_ino_lock);
        return ino;
}

#else

/* On 64 bit simply return ino. */
static inline unsigned long pidfs_ino(u64 ino)
{
        return ino;
}

/* On 64 bit the generation number is 0. */
static inline u32 pidfs_gen(u64 ino)
{
        return 0;
}

DEFINE_COOKIE(pidfs_ino_cookie);

static u64 pidfs_alloc_ino(void)
{
        u64 ino;

        preempt_disable();
        ino = gen_cookie_next(&pidfs_ino_cookie);
        preempt_enable();

        VFS_WARN_ON_ONCE(ino < 1);
        return ino;
}

#endif

void pidfs_prepare_pid(struct pid *pid)
{
        pid->stashed = NULL;
        pid->attr = NULL;
        pid->ino = 0;
}

int pidfs_add_pid(struct pid *pid)
{
        int ret;

        pid->ino = pidfs_alloc_ino();
        ret = rhashtable_insert_fast(&pidfs_ino_ht, &pid->pidfs_hash,
                                     pidfs_ino_ht_params);
        if (unlikely(ret))
                pid->ino = 0;
        return ret;
}

void pidfs_remove_pid(struct pid *pid)
{
        if (likely(pid->ino))
                rhashtable_remove_fast(&pidfs_ino_ht, &pid->pidfs_hash,
                                       pidfs_ino_ht_params);
}

void pidfs_free_pid(struct pid *pid)
{
        struct pidfs_attr *attr __free(kfree) = no_free_ptr(pid->attr);
        struct simple_xattrs *xattrs __free(kfree) = NULL;

        /*
         * Any dentry must've been wiped from the pid by now.
         * Otherwise there's a reference count bug.
         */
        VFS_WARN_ON_ONCE(pid->stashed);

        /*
         * This if an error occurred during e.g., task creation that
         * causes us to never go through the exit path.
         */
        if (unlikely(!attr))
                return;

        /* This never had a pidfd created. */
        if (IS_ERR(attr))
                return;

        xattrs = no_free_ptr(attr->xattrs);
        if (xattrs)
                simple_xattrs_free(xattrs, NULL);
}

#ifdef CONFIG_PROC_FS
/**
 * pidfd_show_fdinfo - print information about a pidfd
 * @m: proc fdinfo file
 * @f: file referencing a pidfd
 *
 * Pid:
 * This function will print the pid that a given pidfd refers to in the
 * pid namespace of the procfs instance.
 * If the pid namespace of the process is not a descendant of the pid
 * namespace of the procfs instance 0 will be shown as its pid. This is
 * similar to calling getppid() on a process whose parent is outside of
 * its pid namespace.
 *
 * NSpid:
 * If pid namespaces are supported then this function will also print
 * the pid of a given pidfd refers to for all descendant pid namespaces
 * starting from the current pid namespace of the instance, i.e. the
 * Pid field and the first entry in the NSpid field will be identical.
 * If the pid namespace of the process is not a descendant of the pid
 * namespace of the procfs instance 0 will be shown as its first NSpid
 * entry and no others will be shown.
 * Note that this differs from the Pid and NSpid fields in
 * /proc/<pid>/status where Pid and NSpid are always shown relative to
 * the  pid namespace of the procfs instance. The difference becomes
 * obvious when sending around a pidfd between pid namespaces from a
 * different branch of the tree, i.e. where no ancestral relation is
 * present between the pid namespaces:
 * - create two new pid namespaces ns1 and ns2 in the initial pid
 *   namespace (also take care to create new mount namespaces in the
 *   new pid namespace and mount procfs)
 * - create a process with a pidfd in ns1
 * - send pidfd from ns1 to ns2
 * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
 *   have exactly one entry, which is 0
 */
static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
{
        struct pid *pid = pidfd_pid(f);
        struct pid_namespace *ns;
        pid_t nr = -1;

        if (likely(pid_has_task(pid, PIDTYPE_PID))) {
                ns = proc_pid_ns(file_inode(m->file)->i_sb);
                nr = pid_nr_ns(pid, ns);
        }

        seq_put_decimal_ll(m, "Pid:\t", nr);

#ifdef CONFIG_PID_NS
        seq_put_decimal_ll(m, "\nNSpid:\t", nr);
        if (nr > 0) {
                int i;

                /* If nr is non-zero it means that 'pid' is valid and that
                 * ns, i.e. the pid namespace associated with the procfs
                 * instance, is in the pid namespace hierarchy of pid.
                 * Start at one below the already printed level.
                 */
                for (i = ns->level + 1; i <= pid->level; i++)
                        seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
        }
#endif
        seq_putc(m, '\n');
}
#endif

/*
 * Poll support for process exit notification.
 */
static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
{
        struct pid *pid = pidfd_pid(file);
        struct task_struct *task;
        __poll_t poll_flags = 0;

        poll_wait(file, &pid->wait_pidfd, pts);
        /*
         * Don't wake waiters if the thread-group leader exited
         * prematurely. They either get notified when the last subthread
         * exits or not at all if one of the remaining subthreads execs
         * and assumes the struct pid of the old thread-group leader.
         */
        guard(rcu)();
        task = pid_task(pid, PIDTYPE_PID);
        if (!task)
                poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
        else if (task->exit_state && !delay_group_leader(task))
                poll_flags = EPOLLIN | EPOLLRDNORM;

        return poll_flags;
}

static inline bool pid_in_current_pidns(const struct pid *pid)
{
        const struct pid_namespace *ns = task_active_pid_ns(current);

        if (ns->level <= pid->level)
                return pid->numbers[ns->level].ns == ns;

        return false;
}

static __u32 pidfs_coredump_mask(unsigned long mm_flags)
{
        switch (__get_dumpable(mm_flags)) {
        case SUID_DUMP_USER:
                return PIDFD_COREDUMP_USER;
        case SUID_DUMP_ROOT:
                return PIDFD_COREDUMP_ROOT;
        case SUID_DUMP_DISABLE:
                return PIDFD_COREDUMP_SKIP;
        default:
                WARN_ON_ONCE(true);
        }

        return 0;
}

/* This must be updated whenever a new flag is added */
#define PIDFD_INFO_SUPPORTED (PIDFD_INFO_PID | \
                              PIDFD_INFO_CREDS | \
                              PIDFD_INFO_CGROUPID | \
                              PIDFD_INFO_EXIT | \
                              PIDFD_INFO_COREDUMP | \
                              PIDFD_INFO_SUPPORTED_MASK | \
                              PIDFD_INFO_COREDUMP_SIGNAL)

static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct pidfd_info __user *uinfo = (struct pidfd_info __user *)arg;
        struct task_struct *task __free(put_task) = NULL;
        struct pid *pid = pidfd_pid(file);
        size_t usize = _IOC_SIZE(cmd);
        struct pidfd_info kinfo = {};
        struct user_namespace *user_ns;
        struct pidfs_attr *attr;
        const struct cred *c;
        __u64 mask;

        BUILD_BUG_ON(sizeof(struct pidfd_info) != PIDFD_INFO_SIZE_VER2);

        if (!uinfo)
                return -EINVAL;
        if (usize < PIDFD_INFO_SIZE_VER0)
                return -EINVAL; /* First version, no smaller struct possible */

        if (copy_from_user(&mask, &uinfo->mask, sizeof(mask)))
                return -EFAULT;

        /*
         * Restrict information retrieval to tasks within the caller's pid
         * namespace hierarchy.
         */
        if (!pid_in_current_pidns(pid))
                return -EREMOTE;

        attr = READ_ONCE(pid->attr);
        if (mask & PIDFD_INFO_EXIT) {
                if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) {
                        smp_rmb();
                        kinfo.mask |= PIDFD_INFO_EXIT;
#ifdef CONFIG_CGROUPS
                        kinfo.cgroupid = attr->cgroupid;
                        kinfo.mask |= PIDFD_INFO_CGROUPID;
#endif
                        kinfo.exit_code = attr->exit_code;
                }
        }

        if (mask & PIDFD_INFO_COREDUMP) {
                if (test_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) {
                        smp_rmb();
                        kinfo.mask |= PIDFD_INFO_COREDUMP | PIDFD_INFO_COREDUMP_SIGNAL;
                        kinfo.coredump_mask = attr->coredump_mask;
                        kinfo.coredump_signal = attr->coredump_signal;
                }
        }

        task = get_pid_task(pid, PIDTYPE_PID);
        if (!task) {
                /*
                 * If the task has already been reaped, only exit
                 * information is available
                 */
                if (!(mask & PIDFD_INFO_EXIT))
                        return -ESRCH;

                goto copy_out;
        }

        c = get_task_cred(task);
        if (!c)
                return -ESRCH;

        if ((mask & PIDFD_INFO_COREDUMP) && !kinfo.coredump_mask) {
                guard(task_lock)(task);
                if (task->mm) {
                        unsigned long flags = __mm_flags_get_dumpable(task->mm);

                        kinfo.coredump_mask = pidfs_coredump_mask(flags);
                        kinfo.mask |= PIDFD_INFO_COREDUMP;
                        /* No coredump actually took place, so no coredump signal. */
                }
        }

        /* Unconditionally return identifiers and credentials, the rest only on request */

        user_ns = current_user_ns();
        kinfo.ruid = from_kuid_munged(user_ns, c->uid);
        kinfo.rgid = from_kgid_munged(user_ns, c->gid);
        kinfo.euid = from_kuid_munged(user_ns, c->euid);
        kinfo.egid = from_kgid_munged(user_ns, c->egid);
        kinfo.suid = from_kuid_munged(user_ns, c->suid);
        kinfo.sgid = from_kgid_munged(user_ns, c->sgid);
        kinfo.fsuid = from_kuid_munged(user_ns, c->fsuid);
        kinfo.fsgid = from_kgid_munged(user_ns, c->fsgid);
        kinfo.mask |= PIDFD_INFO_CREDS;
        put_cred(c);

#ifdef CONFIG_CGROUPS
        if (!kinfo.cgroupid) {
                struct cgroup *cgrp;

                rcu_read_lock();
                cgrp = task_dfl_cgroup(task);
                kinfo.cgroupid = cgroup_id(cgrp);
                kinfo.mask |= PIDFD_INFO_CGROUPID;
                rcu_read_unlock();
        }
#endif

        /*
         * Copy pid/tgid last, to reduce the chances the information might be
         * stale. Note that it is not possible to ensure it will be valid as the
         * task might return as soon as the copy_to_user finishes, but that's ok
         * and userspace expects that might happen and can act accordingly, so
         * this is just best-effort. What we can do however is checking that all
         * the fields are set correctly, or return ESRCH to avoid providing
         * incomplete information. */

        kinfo.ppid = task_ppid_vnr(task);
        kinfo.tgid = task_tgid_vnr(task);
        kinfo.pid = task_pid_vnr(task);
        kinfo.mask |= PIDFD_INFO_PID;

        if (kinfo.pid == 0 || kinfo.tgid == 0)
                return -ESRCH;

copy_out:
        if (mask & PIDFD_INFO_SUPPORTED_MASK) {
                kinfo.mask |= PIDFD_INFO_SUPPORTED_MASK;
                kinfo.supported_mask = PIDFD_INFO_SUPPORTED;
        }

        /* Are there bits in the return mask not present in PIDFD_INFO_SUPPORTED? */
        WARN_ON_ONCE(~PIDFD_INFO_SUPPORTED & kinfo.mask);
        /*
         * If userspace and the kernel have the same struct size it can just
         * be copied. If userspace provides an older struct, only the bits that
         * userspace knows about will be copied. If userspace provides a new
         * struct, only the bits that the kernel knows about will be copied.
         */
        return copy_struct_to_user(uinfo, usize, &kinfo, sizeof(kinfo), NULL);
}

static bool pidfs_ioctl_valid(unsigned int cmd)
{
        switch (cmd) {
        case FS_IOC_GETVERSION:
        case PIDFD_GET_CGROUP_NAMESPACE:
        case PIDFD_GET_IPC_NAMESPACE:
        case PIDFD_GET_MNT_NAMESPACE:
        case PIDFD_GET_NET_NAMESPACE:
        case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
        case PIDFD_GET_TIME_NAMESPACE:
        case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
        case PIDFD_GET_UTS_NAMESPACE:
        case PIDFD_GET_USER_NAMESPACE:
        case PIDFD_GET_PID_NAMESPACE:
                return true;
        }

        /* Extensible ioctls require some more careful checks. */
        switch (_IOC_NR(cmd)) {
        case _IOC_NR(PIDFD_GET_INFO):
                /*
                 * Try to prevent performing a pidfd ioctl when someone
                 * erronously mistook the file descriptor for a pidfd.
                 * This is not perfect but will catch most cases.
                 */
                return extensible_ioctl_valid(cmd, PIDFD_GET_INFO, PIDFD_INFO_SIZE_VER0);
        }

        return false;
}

static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct task_struct *task __free(put_task) = NULL;
        struct nsproxy *nsp __free(put_nsproxy) = NULL;
        struct ns_common *ns_common = NULL;

        if (!pidfs_ioctl_valid(cmd))
                return -ENOIOCTLCMD;

        if (cmd == FS_IOC_GETVERSION) {
                if (!arg)
                        return -EINVAL;

                __u32 __user *argp = (__u32 __user *)arg;
                return put_user(file_inode(file)->i_generation, argp);
        }

        /* Extensible IOCTL that does not open namespace FDs, take a shortcut */
        if (_IOC_NR(cmd) == _IOC_NR(PIDFD_GET_INFO))
                return pidfd_info(file, cmd, arg);

        task = get_pid_task(pidfd_pid(file), PIDTYPE_PID);
        if (!task)
                return -ESRCH;

        if (arg)
                return -EINVAL;

        scoped_guard(task_lock, task) {
                nsp = task->nsproxy;
                if (nsp)
                        get_nsproxy(nsp);
        }
        if (!nsp)
                return -ESRCH; /* just pretend it didn't exist */

        /*
         * We're trying to open a file descriptor to the namespace so perform a
         * filesystem cred ptrace check. Also, we mirror nsfs behavior.
         */
        if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
                return -EACCES;

        switch (cmd) {
        /* Namespaces that hang of nsproxy. */
        case PIDFD_GET_CGROUP_NAMESPACE:
#ifdef CONFIG_CGROUPS
                if (!ns_ref_get(nsp->cgroup_ns))
                        break;
                ns_common = to_ns_common(nsp->cgroup_ns);
#endif
                break;
        case PIDFD_GET_IPC_NAMESPACE:
#ifdef CONFIG_IPC_NS
                if (!ns_ref_get(nsp->ipc_ns))
                        break;
                ns_common = to_ns_common(nsp->ipc_ns);
#endif
                break;
        case PIDFD_GET_MNT_NAMESPACE:
                if (!ns_ref_get(nsp->mnt_ns))
                        break;
                ns_common = to_ns_common(nsp->mnt_ns);
                break;
        case PIDFD_GET_NET_NAMESPACE:
#ifdef CONFIG_NET_NS
                if (!ns_ref_get(nsp->net_ns))
                        break;
                ns_common = to_ns_common(nsp->net_ns);
#endif
                break;
        case PIDFD_GET_PID_FOR_CHILDREN_NAMESPACE:
#ifdef CONFIG_PID_NS
                if (!ns_ref_get(nsp->pid_ns_for_children))
                        break;
                ns_common = to_ns_common(nsp->pid_ns_for_children);
#endif
                break;
        case PIDFD_GET_TIME_NAMESPACE:
#ifdef CONFIG_TIME_NS
                if (!ns_ref_get(nsp->time_ns))
                        break;
                ns_common = to_ns_common(nsp->time_ns);
#endif
                break;
        case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
#ifdef CONFIG_TIME_NS
                if (!ns_ref_get(nsp->time_ns_for_children))
                        break;
                ns_common = to_ns_common(nsp->time_ns_for_children);
#endif
                break;
        case PIDFD_GET_UTS_NAMESPACE:
#ifdef CONFIG_UTS_NS
                if (!ns_ref_get(nsp->uts_ns))
                        break;
                ns_common = to_ns_common(nsp->uts_ns);
#endif
                break;
        /* Namespaces that don't hang of nsproxy. */
        case PIDFD_GET_USER_NAMESPACE:
#ifdef CONFIG_USER_NS
                scoped_guard(rcu) {
                        struct user_namespace *user_ns;

                        user_ns = task_cred_xxx(task, user_ns);
                        if (ns_ref_get(user_ns))
                                ns_common = to_ns_common(user_ns);
                }
#endif
                break;
        case PIDFD_GET_PID_NAMESPACE:
#ifdef CONFIG_PID_NS
                scoped_guard(rcu) {
                        struct pid_namespace *pid_ns;

                        pid_ns = task_active_pid_ns(task);
                        if (ns_ref_get(pid_ns))
                                ns_common = to_ns_common(pid_ns);
                }
#endif
                break;
        default:
                return -ENOIOCTLCMD;
        }

        if (!ns_common)
                return -EOPNOTSUPP;

        /* open_namespace() unconditionally consumes the reference */
        return open_namespace(ns_common);
}

static const struct file_operations pidfs_file_operations = {
        .poll           = pidfd_poll,
#ifdef CONFIG_PROC_FS
        .show_fdinfo    = pidfd_show_fdinfo,
#endif
        .unlocked_ioctl = pidfd_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
};

struct pid *pidfd_pid(const struct file *file)
{
        if (file->f_op != &pidfs_file_operations)
                return ERR_PTR(-EBADF);
        return file_inode(file)->i_private;
}

/*
 * We're called from release_task(). We know there's at least one
 * reference to struct pid being held that won't be released until the
 * task has been reaped which cannot happen until we're out of
 * release_task().
 *
 * If this struct pid has at least once been referred to by a pidfd then
 * pid->attr will be allocated. If not we mark the struct pid as dead so
 * anyone who is trying to register it with pidfs will fail to do so.
 * Otherwise we would hand out pidfs for reaped tasks without having
 * exit information available.
 *
 * Worst case is that we've filled in the info and the pid gets freed
 * right away in free_pid() when no one holds a pidfd anymore. Since
 * pidfs_exit() currently is placed after exit_task_work() we know that
 * it cannot be us aka the exiting task holding a pidfd to itself.
 */
void pidfs_exit(struct task_struct *tsk)
{
        struct pid *pid = task_pid(tsk);
        struct pidfs_attr *attr;
#ifdef CONFIG_CGROUPS
        struct cgroup *cgrp;
#endif

        might_sleep();

        /* Synchronize with pidfs_register_pid(). */
        scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
                attr = pid->attr;
                if (!attr) {
                        /*
                         * No one ever held a pidfd for this struct pid.
                         * Mark it as dead so no one can add a pidfs
                         * entry anymore. We're about to be reaped and
                         * so no exit information would be available.
                         */
                        pid->attr = PIDFS_PID_DEAD;
                        return;
                }
        }

        /*
         * If @pid->attr is set someone might still legitimately hold a
         * pidfd to @pid or someone might concurrently still be getting
         * a reference to an already stashed dentry from @pid->stashed.
         * So defer cleaning @pid->attr until the last reference to @pid
         * is put
         */

#ifdef CONFIG_CGROUPS
        rcu_read_lock();
        cgrp = task_dfl_cgroup(tsk);
        attr->cgroupid = cgroup_id(cgrp);
        rcu_read_unlock();
#endif
        attr->exit_code = tsk->exit_code;

        /* Ensure that PIDFD_GET_INFO sees either all or nothing. */
        smp_wmb();
        set_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask);
}

#ifdef CONFIG_COREDUMP
void pidfs_coredump(const struct coredump_params *cprm)
{
        struct pid *pid = cprm->pid;
        struct pidfs_attr *attr;

        attr = READ_ONCE(pid->attr);

        VFS_WARN_ON_ONCE(!attr);
        VFS_WARN_ON_ONCE(attr == PIDFS_PID_DEAD);

        /* Note how we were coredumped and that we coredumped. */
        attr->coredump_mask = pidfs_coredump_mask(cprm->mm_flags) |
                              PIDFD_COREDUMPED;
        /* If coredumping is set to skip we should never end up here. */
        VFS_WARN_ON_ONCE(attr->coredump_mask & PIDFD_COREDUMP_SKIP);
        /* Expose the signal number that caused the coredump. */
        attr->coredump_signal = cprm->siginfo->si_signo;
        smp_wmb();
        set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask);
}
#endif

static struct vfsmount *pidfs_mnt __ro_after_init;

/*
 * The vfs falls back to simple_setattr() if i_op->setattr() isn't
 * implemented. Let's reject it completely until we have a clean
 * permission concept for pidfds.
 */
static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
                         struct iattr *attr)
{
        return anon_inode_setattr(idmap, dentry, attr);
}

static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
                         struct kstat *stat, u32 request_mask,
                         unsigned int query_flags)
{
        return anon_inode_getattr(idmap, path, stat, request_mask, query_flags);
}

static ssize_t pidfs_listxattr(struct dentry *dentry, char *buf, size_t size)
{
        struct inode *inode = d_inode(dentry);
        struct pid *pid = inode->i_private;
        struct pidfs_attr *attr = pid->attr;
        struct simple_xattrs *xattrs;

        xattrs = READ_ONCE(attr->xattrs);
        if (!xattrs)
                return 0;

        return simple_xattr_list(inode, xattrs, buf, size);
}

static const struct inode_operations pidfs_inode_operations = {
        .getattr        = pidfs_getattr,
        .setattr        = pidfs_setattr,
        .listxattr      = pidfs_listxattr,
};

static void pidfs_evict_inode(struct inode *inode)
{
        struct pid *pid = inode->i_private;

        clear_inode(inode);
        put_pid(pid);
}

static const struct super_operations pidfs_sops = {
        .drop_inode     = inode_just_drop,
        .evict_inode    = pidfs_evict_inode,
        .statfs         = simple_statfs,
};

/*
 * 'lsof' has knowledge of out historical anon_inode use, and expects
 * the pidfs dentry name to start with 'anon_inode'.
 */
static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
{
        return dynamic_dname(buffer, buflen, "anon_inode:[pidfd]");
}

const struct dentry_operations pidfs_dentry_operations = {
        .d_dname        = pidfs_dname,
        .d_prune        = stashed_dentry_prune,
};

static int pidfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
                           struct inode *parent)
{
        const struct pid *pid = inode->i_private;

        if (*max_len < 2) {
                *max_len = 2;
                return FILEID_INVALID;
        }

        *max_len = 2;
        *(u64 *)fh = pid->ino;
        return FILEID_KERNFS;
}

/* Find a struct pid based on the inode number. */
static struct pid *pidfs_ino_get_pid(u64 ino)
{
        struct pid *pid;
        struct pidfs_attr *attr;

        guard(rcu)();
        pid = rhashtable_lookup(&pidfs_ino_ht, &ino, pidfs_ino_ht_params);
        if (!pid)
                return NULL;
        attr = READ_ONCE(pid->attr);
        if (IS_ERR_OR_NULL(attr))
                return NULL;
        if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask))
                return NULL;
        /* Within our pid namespace hierarchy? */
        if (pid_vnr(pid) == 0)
                return NULL;
        return get_pid(pid);
}

static struct dentry *pidfs_fh_to_dentry(struct super_block *sb,
                                         struct fid *fid, int fh_len,
                                         int fh_type)
{
        int ret;
        u64 pid_ino;
        struct path path;
        struct pid *pid;

        if (fh_len < 2)
                return NULL;

        switch (fh_type) {
        case FILEID_KERNFS:
                pid_ino = *(u64 *)fid;
                break;
        default:
                return NULL;
        }

        pid = pidfs_ino_get_pid(pid_ino);
        if (!pid)
                return NULL;

        ret = path_from_stashed(&pid->stashed, pidfs_mnt, pid, &path);
        if (ret < 0)
                return ERR_PTR(ret);

        VFS_WARN_ON_ONCE(!pid->attr);

        mntput(path.mnt);
        return path.dentry;
}

/*
 * Make sure that we reject any nonsensical flags that users pass via
 * open_by_handle_at(). Note that PIDFD_THREAD is defined as O_EXCL, and
 * PIDFD_NONBLOCK as O_NONBLOCK.
 */
#define VALID_FILE_HANDLE_OPEN_FLAGS \
        (O_RDONLY | O_WRONLY | O_RDWR | O_NONBLOCK | O_CLOEXEC | O_EXCL)

static int pidfs_export_permission(struct handle_to_path_ctx *ctx,
                                   unsigned int oflags)
{
        if (oflags & ~(VALID_FILE_HANDLE_OPEN_FLAGS | O_LARGEFILE))
                return -EINVAL;

        /*
         * pidfd_ino_get_pid() will verify that the struct pid is part
         * of the caller's pid namespace hierarchy. No further
         * permission checks are needed.
         */
        return 0;
}

static struct file *pidfs_export_open(const struct path *path, unsigned int oflags)
{
        /*
         * Clear O_LARGEFILE as open_by_handle_at() forces it and raise
         * O_RDWR as pidfds always are.
         */
        oflags &= ~O_LARGEFILE;
        return dentry_open(path, oflags | O_RDWR, current_cred());
}

static const struct export_operations pidfs_export_operations = {
        .encode_fh      = pidfs_encode_fh,
        .fh_to_dentry   = pidfs_fh_to_dentry,
        .open           = pidfs_export_open,
        .permission     = pidfs_export_permission,
};

static int pidfs_init_inode(struct inode *inode, void *data)
{
        const struct pid *pid = data;

        inode->i_private = data;
        inode->i_flags |= S_PRIVATE | S_ANON_INODE;
        /* We allow to set xattrs. */
        inode->i_flags &= ~S_IMMUTABLE;
        inode->i_mode |= S_IRWXU;
        inode->i_op = &pidfs_inode_operations;
        inode->i_fop = &pidfs_file_operations;
        inode->i_ino = pidfs_ino(pid->ino);
        inode->i_generation = pidfs_gen(pid->ino);
        return 0;
}

static void pidfs_put_data(void *data)
{
        struct pid *pid = data;
        put_pid(pid);
}

/**
 * pidfs_register_pid - register a struct pid in pidfs
 * @pid: pid to pin
 *
 * Register a struct pid in pidfs.
 *
 * Return: On success zero, on error a negative error code is returned.
 */
int pidfs_register_pid(struct pid *pid)
{
        struct pidfs_attr *new_attr __free(kfree) = NULL;
        struct pidfs_attr *attr;

        might_sleep();

        if (!pid)
                return 0;

        attr = READ_ONCE(pid->attr);
        if (unlikely(attr == PIDFS_PID_DEAD))
                return PTR_ERR(PIDFS_PID_DEAD);
        if (attr)
                return 0;

        new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL);
        if (!new_attr)
                return -ENOMEM;

        /* Synchronize with pidfs_exit(). */
        guard(spinlock_irq)(&pid->wait_pidfd.lock);

        attr = pid->attr;
        if (unlikely(attr == PIDFS_PID_DEAD))
                return PTR_ERR(PIDFS_PID_DEAD);
        if (unlikely(attr))
                return 0;

        pid->attr = no_free_ptr(new_attr);
        return 0;
}

static struct dentry *pidfs_stash_dentry(struct dentry **stashed,
                                         struct dentry *dentry)
{
        int ret;
        struct pid *pid = d_inode(dentry)->i_private;

        VFS_WARN_ON_ONCE(stashed != &pid->stashed);

        ret = pidfs_register_pid(pid);
        if (ret)
                return ERR_PTR(ret);

        return stash_dentry(stashed, dentry);
}

static const struct stashed_operations pidfs_stashed_ops = {
        .stash_dentry   = pidfs_stash_dentry,
        .init_inode     = pidfs_init_inode,
        .put_data       = pidfs_put_data,
};

static int pidfs_xattr_get(const struct xattr_handler *handler,
                           struct dentry *unused, struct inode *inode,
                           const char *suffix, void *value, size_t size)
{
        struct pid *pid = inode->i_private;
        struct pidfs_attr *attr = pid->attr;
        const char *name;
        struct simple_xattrs *xattrs;

        xattrs = READ_ONCE(attr->xattrs);
        if (!xattrs)
                return 0;

        name = xattr_full_name(handler, suffix);
        return simple_xattr_get(xattrs, name, value, size);
}

static int pidfs_xattr_set(const struct xattr_handler *handler,
                           struct mnt_idmap *idmap, struct dentry *unused,
                           struct inode *inode, const char *suffix,
                           const void *value, size_t size, int flags)
{
        struct pid *pid = inode->i_private;
        struct pidfs_attr *attr = pid->attr;
        const char *name;
        struct simple_xattrs *xattrs;
        struct simple_xattr *old_xattr;

        /* Ensure we're the only one to set @attr->xattrs. */
        WARN_ON_ONCE(!inode_is_locked(inode));

        xattrs = READ_ONCE(attr->xattrs);
        if (!xattrs) {
                xattrs = kmem_cache_zalloc(pidfs_xattr_cachep, GFP_KERNEL);
                if (!xattrs)
                        return -ENOMEM;

                simple_xattrs_init(xattrs);
                smp_store_release(&pid->attr->xattrs, xattrs);
        }

        name = xattr_full_name(handler, suffix);
        old_xattr = simple_xattr_set(xattrs, name, value, size, flags);
        if (IS_ERR(old_xattr))
                return PTR_ERR(old_xattr);

        simple_xattr_free(old_xattr);
        return 0;
}

static const struct xattr_handler pidfs_trusted_xattr_handler = {
        .prefix = XATTR_TRUSTED_PREFIX,
        .get    = pidfs_xattr_get,
        .set    = pidfs_xattr_set,
};

static const struct xattr_handler *const pidfs_xattr_handlers[] = {
        &pidfs_trusted_xattr_handler,
        NULL
};

static int pidfs_init_fs_context(struct fs_context *fc)
{
        struct pseudo_fs_context *ctx;

        ctx = init_pseudo(fc, PID_FS_MAGIC);
        if (!ctx)
                return -ENOMEM;

        fc->s_iflags |= SB_I_NOEXEC;
        fc->s_iflags |= SB_I_NODEV;
        ctx->s_d_flags |= DCACHE_DONTCACHE;
        ctx->ops = &pidfs_sops;
        ctx->eops = &pidfs_export_operations;
        ctx->dops = &pidfs_dentry_operations;
        ctx->xattr = pidfs_xattr_handlers;
        fc->s_fs_info = (void *)&pidfs_stashed_ops;
        return 0;
}

static struct file_system_type pidfs_type = {
        .name                   = "pidfs",
        .init_fs_context        = pidfs_init_fs_context,
        .kill_sb                = kill_anon_super,
};

struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
{
        struct file *pidfd_file;
        struct path path __free(path_put) = {};
        int ret;

        /*
         * Ensure that PIDFD_STALE can be passed as a flag without
         * overloading other uapi pidfd flags.
         */
        BUILD_BUG_ON(PIDFD_STALE == PIDFD_THREAD);
        BUILD_BUG_ON(PIDFD_STALE == PIDFD_NONBLOCK);

        ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
        if (ret < 0)
                return ERR_PTR(ret);

        VFS_WARN_ON_ONCE(!pid->attr);

        flags &= ~PIDFD_STALE;
        flags |= O_RDWR;
        pidfd_file = dentry_open(&path, flags, current_cred());
        /* Raise PIDFD_THREAD explicitly as do_dentry_open() strips it. */
        if (!IS_ERR(pidfd_file))
                pidfd_file->f_flags |= (flags & PIDFD_THREAD);

        return pidfd_file;
}

void __init pidfs_init(void)
{
        if (rhashtable_init(&pidfs_ino_ht, &pidfs_ino_ht_params))
                panic("Failed to initialize pidfs hashtable");

        pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0,
                                         (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
                                          SLAB_ACCOUNT | SLAB_PANIC), NULL);

        pidfs_xattr_cachep = kmem_cache_create("pidfs_xattr_cache",
                                               sizeof(struct simple_xattrs), 0,
                                               (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
                                                SLAB_ACCOUNT | SLAB_PANIC), NULL);

        pidfs_mnt = kern_mount(&pidfs_type);
        if (IS_ERR(pidfs_mnt))
                panic("Failed to mount pidfs pseudo filesystem");

        pidfs_root_path.mnt = pidfs_mnt;
        pidfs_root_path.dentry = pidfs_mnt->mnt_root;
}