// SPDX-License-Identifier: GPL-2.0
#include <linux/sched/signal.h>
#include <linux/errno.h>
#include <linux/dcache.h>
#include <linux/path.h>
#include <linux/fdtable.h>
#include <linux/namei.h>
#include <linux/pid.h>
#include <linux/ptrace.h>
#include <linux/bitmap.h>
#include <linux/security.h>
#include <linux/file.h>
#include <linux/seq_file.h>
#include <linux/fs.h>
#include <linux/filelock.h>

#include <linux/proc_fs.h>

#include "../mount.h"
#include "internal.h"
#include "fd.h"

static int seq_show(struct seq_file *m, void *v)
{
        struct files_struct *files = NULL;
        int f_flags = 0, ret = -ENOENT;
        struct file *file = NULL;
        struct task_struct *task;

        task = get_proc_task(m->private);
        if (!task)
                return -ENOENT;

        task_lock(task);
        files = task->files;
        if (files) {
                unsigned int fd = proc_fd(m->private);

                spin_lock(&files->file_lock);
                file = files_lookup_fd_locked(files, fd);
                if (file) {
                        f_flags = file->f_flags;
                        if (close_on_exec(fd, files))
                                f_flags |= O_CLOEXEC;

                        get_file(file);
                        ret = 0;
                }
                spin_unlock(&files->file_lock);
        }
        task_unlock(task);
        put_task_struct(task);

        if (ret)
                return ret;

        seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\n",
                   (long long)file->f_pos, f_flags,
                   real_mount(file->f_path.mnt)->mnt_id,
                   file_inode(file)->i_ino);

        /* show_fd_locks() never dereferences files, so a stale value is safe */
        show_fd_locks(m, file, files);
        if (seq_has_overflowed(m))
                goto out;

        if (file->f_op->show_fdinfo)
                file->f_op->show_fdinfo(m, file);

out:
        fput(file);
        return 0;
}

static int seq_fdinfo_open(struct inode *inode, struct file *file)
{
        return single_open(file, seq_show, inode);
}

/*
 * Shared /proc/pid/fdinfo and /proc/pid/fdinfo/fd permission helper to ensure
 * that the current task has PTRACE_MODE_READ in addition to the normal
 * POSIX-like checks.
 */
static int proc_fdinfo_permission(struct mnt_idmap *idmap, struct inode *inode,
                                  int mask)
{
        bool allowed = false;
        struct task_struct *task = get_proc_task(inode);

        if (!task)
                return -ESRCH;

        allowed = ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
        put_task_struct(task);

        if (!allowed)
                return -EACCES;

        return generic_permission(idmap, inode, mask);
}

static const struct inode_operations proc_fdinfo_file_inode_operations = {
        .permission     = proc_fdinfo_permission,
        .setattr        = proc_setattr,
};

static const struct file_operations proc_fdinfo_file_operations = {
        .open           = seq_fdinfo_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static bool tid_fd_mode(struct task_struct *task, unsigned fd, fmode_t *mode)
{
        struct file *file;

        file = fget_task(task, fd);
        if (file) {
                *mode = file->f_mode;
                fput(file);
        }
        return !!file;
}

static void tid_fd_update_inode(struct task_struct *task, struct inode *inode,
                                fmode_t f_mode)
{
        task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);

        if (S_ISLNK(inode->i_mode)) {
                unsigned i_mode = S_IFLNK;
                if (f_mode & FMODE_READ)
                        i_mode |= S_IRUSR | S_IXUSR;
                if (f_mode & FMODE_WRITE)
                        i_mode |= S_IWUSR | S_IXUSR;
                inode->i_mode = i_mode;
        }
        security_task_to_inode(task, inode);
}

static int tid_fd_revalidate(struct inode *dir, const struct qstr *name,
                             struct dentry *dentry, unsigned int flags)
{
        struct task_struct *task;
        struct inode *inode;
        unsigned int fd;

        if (flags & LOOKUP_RCU)
                return -ECHILD;

        inode = d_inode(dentry);
        task = get_proc_task(inode);
        fd = proc_fd(inode);

        if (task) {
                fmode_t f_mode;
                if (tid_fd_mode(task, fd, &f_mode)) {
                        tid_fd_update_inode(task, inode, f_mode);
                        put_task_struct(task);
                        return 1;
                }
                put_task_struct(task);
        }
        return 0;
}

static const struct dentry_operations tid_fd_dentry_operations = {
        .d_revalidate   = tid_fd_revalidate,
        .d_delete       = pid_delete_dentry,
};

static int proc_fd_link(struct dentry *dentry, struct path *path)
{
        struct task_struct *task;
        int ret = -ENOENT;

        task = get_proc_task(d_inode(dentry));
        if (task) {
                unsigned int fd = proc_fd(d_inode(dentry));
                struct file *fd_file;

                fd_file = fget_task(task, fd);
                if (fd_file) {
                        *path = fd_file->f_path;
                        path_get(&fd_file->f_path);
                        ret = 0;
                        fput(fd_file);
                }
                put_task_struct(task);
        }

        return ret;
}

struct fd_data {
        fmode_t mode;
        unsigned fd;
};

static struct dentry *proc_fd_instantiate(struct dentry *dentry,
        struct task_struct *task, const void *ptr)
{
        const struct fd_data *data = ptr;
        struct proc_inode *ei;
        struct inode *inode;

        inode = proc_pid_make_inode(dentry->d_sb, task, S_IFLNK);
        if (!inode)
                return ERR_PTR(-ENOENT);

        ei = PROC_I(inode);
        ei->fd = data->fd;

        inode->i_op = &proc_pid_link_inode_operations;
        inode->i_size = 64;

        ei->op.proc_get_link = proc_fd_link;
        tid_fd_update_inode(task, inode, data->mode);

        return proc_splice_unmountable(inode, dentry,
                                       &tid_fd_dentry_operations);
}

static struct dentry *proc_lookupfd_common(struct inode *dir,
                                           struct dentry *dentry,
                                           instantiate_t instantiate)
{
        struct task_struct *task = get_proc_task(dir);
        struct fd_data data = {.fd = name_to_int(&dentry->d_name)};
        struct dentry *result = ERR_PTR(-ENOENT);

        if (!task)
                goto out_no_task;
        if (data.fd == ~0U)
                goto out;
        if (!tid_fd_mode(task, data.fd, &data.mode))
                goto out;

        result = instantiate(dentry, task, &data);
out:
        put_task_struct(task);
out_no_task:
        return result;
}

static int proc_readfd_common(struct file *file, struct dir_context *ctx,
                              instantiate_t instantiate)
{
        struct task_struct *p = get_proc_task(file_inode(file));
        unsigned int fd;

        if (!p)
                return -ENOENT;

        if (!dir_emit_dots(file, ctx))
                goto out;

        for (fd = ctx->pos - 2;; fd++) {
                struct file *f;
                struct fd_data data;
                char name[10 + 1];
                unsigned int len;

                f = fget_task_next(p, &fd);
                ctx->pos = fd + 2LL;
                if (!f)
                        break;
                data.mode = f->f_mode;
                fput(f);
                data.fd = fd;

                len = snprintf(name, sizeof(name), "%u", fd);
                if (!proc_fill_cache(file, ctx,
                                     name, len, instantiate, p,
                                     &data))
                        break;
                cond_resched();
        }
out:
        put_task_struct(p);
        return 0;
}

static int proc_readfd_count(struct inode *inode, loff_t *count)
{
        struct task_struct *p = get_proc_task(inode);
        struct fdtable *fdt;

        if (!p)
                return -ENOENT;

        task_lock(p);
        if (p->files) {
                rcu_read_lock();

                fdt = files_fdtable(p->files);
                *count = bitmap_weight(fdt->open_fds, fdt->max_fds);

                rcu_read_unlock();
        }
        task_unlock(p);

        put_task_struct(p);

        return 0;
}

static int proc_fd_iterate(struct file *file, struct dir_context *ctx)
{
        return proc_readfd_common(file, ctx, proc_fd_instantiate);
}

const struct file_operations proc_fd_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_fd_iterate,
        .llseek         = generic_file_llseek,
};

static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
                                    unsigned int flags)
{
        return proc_lookupfd_common(dir, dentry, proc_fd_instantiate);
}

/*
 * /proc/pid/fd needs a special permission handler so that a process can still
 * access /proc/self/fd after it has executed a setuid().
 */
int proc_fd_permission(struct mnt_idmap *idmap,
                       struct inode *inode, int mask)
{
        struct task_struct *p;
        int rv;

        rv = generic_permission(&nop_mnt_idmap, inode, mask);
        if (rv == 0)
                return rv;

        rcu_read_lock();
        p = pid_task(proc_pid(inode), PIDTYPE_PID);
        if (p && same_thread_group(p, current))
                rv = 0;
        rcu_read_unlock();

        return rv;
}

static int proc_fd_getattr(struct mnt_idmap *idmap,
                        const struct path *path, struct kstat *stat,
                        u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = d_inode(path->dentry);

        generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
        return proc_readfd_count(inode, &stat->size);
}

const struct inode_operations proc_fd_inode_operations = {
        .lookup         = proc_lookupfd,
        .permission     = proc_fd_permission,
        .getattr        = proc_fd_getattr,
        .setattr        = proc_setattr,
};

static struct dentry *proc_fdinfo_instantiate(struct dentry *dentry,
        struct task_struct *task, const void *ptr)
{
        const struct fd_data *data = ptr;
        struct proc_inode *ei;
        struct inode *inode;

        inode = proc_pid_make_inode(dentry->d_sb, task, S_IFREG | S_IRUGO);
        if (!inode)
                return ERR_PTR(-ENOENT);

        ei = PROC_I(inode);
        ei->fd = data->fd;

        inode->i_op = &proc_fdinfo_file_inode_operations;

        inode->i_fop = &proc_fdinfo_file_operations;
        tid_fd_update_inode(task, inode, 0);

        return proc_splice_unmountable(inode, dentry,
                                       &tid_fd_dentry_operations);
}

static struct dentry *
proc_lookupfdinfo(struct inode *dir, struct dentry *dentry, unsigned int flags)
{
        return proc_lookupfd_common(dir, dentry, proc_fdinfo_instantiate);
}

static int proc_fdinfo_iterate(struct file *file, struct dir_context *ctx)
{
        return proc_readfd_common(file, ctx,
                                  proc_fdinfo_instantiate);
}

const struct inode_operations proc_fdinfo_inode_operations = {
        .lookup         = proc_lookupfdinfo,
        .permission     = proc_fdinfo_permission,
        .setattr        = proc_setattr,
};

const struct file_operations proc_fdinfo_operations = {
        .read           = generic_read_dir,
        .iterate_shared = proc_fdinfo_iterate,
        .llseek         = generic_file_llseek,
};