// SPDX-License-Identifier: GPL-2.0
/*
 * Provide access to virtual console memory.
 * /dev/vcs: the screen as it is being viewed right now (possibly scrolled)
 * /dev/vcsN: the screen of /dev/ttyN (1 <= N <= 63)
 *            [minor: N]
 *
 * /dev/vcsaN: idem, but including attributes, and prefixed with
 *      the 4 bytes lines,columns,x,y (as screendump used to give).
 *      Attribute/character pair is in native endianity.
 *            [minor: N+128]
 *
 * /dev/vcsuN: similar to /dev/vcsaN but using 4-byte unicode values
 *      instead of 1-byte screen glyph values.
 *            [minor: N+64]
 *
 * /dev/vcsuaN: same idea as /dev/vcsaN for unicode (not yet implemented).
 *
 * This replaces screendump and part of selection, so that the system
 * administrator can control access using file system permissions.
 *
 * aeb@cwi.nl - efter Friedas begravelse - 950211
 *
 * machek@k332.feld.cvut.cz - modified not to send characters to wrong console
 *       - fixed some fatal off-by-one bugs (0-- no longer == -1 -> looping and looping and looping...)
 *       - making it shorter - scr_readw are macros which expand in PRETTY long code
 */

#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/tty.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/vt_kern.h>
#include <linux/selection.h>
#include <linux/kbd_kern.h>
#include <linux/console.h>
#include <linux/device.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/signal.h>
#include <linux/slab.h>
#include <linux/notifier.h>

#include <linux/uaccess.h>
#include <asm/byteorder.h>
#include <linux/unaligned.h>

#define HEADER_SIZE     4u
#define CON_BUF_SIZE (IS_ENABLED(CONFIG_BASE_SMALL) ? 256 : PAGE_SIZE)

DEFINE_FREE(free_page_ptr, void *, if (_T) free_page((unsigned long)_T));

/*
 * Our minor space:
 *
 *   0 ... 63   glyph mode without attributes
 *  64 ... 127  unicode mode without attributes
 * 128 ... 191  glyph mode with attributes
 * 192 ... 255  unused (reserved for unicode with attributes)
 *
 * This relies on MAX_NR_CONSOLES being  <= 63, meaning 63 actual consoles
 * with minors 0, 64, 128 and 192 being proxies for the foreground console.
 */
#if MAX_NR_CONSOLES > 63
#warning "/dev/vcs* devices may not accommodate more than 63 consoles"
#endif

#define console(inode)          (iminor(inode) & 63)
#define use_unicode(inode)      (iminor(inode) & 64)
#define use_attributes(inode)   (iminor(inode) & 128)

struct vcs_poll_data {
        struct notifier_block notifier;
        unsigned int cons_num;
        int event;
        wait_queue_head_t waitq;
        struct fasync_struct *fasync;
};

static int
vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
{
        struct vt_notifier_param *param = _param;
        struct vc_data *vc = param->vc;
        struct vcs_poll_data *poll =
                container_of(nb, struct vcs_poll_data, notifier);
        int currcons = poll->cons_num;
        int fa_band;

        switch (code) {
        case VT_UPDATE:
                fa_band = POLL_PRI;
                break;
        case VT_DEALLOCATE:
                fa_band = POLL_HUP;
                break;
        default:
                return NOTIFY_DONE;
        }

        if (currcons == 0)
                currcons = fg_console;
        else
                currcons--;
        if (currcons != vc->vc_num)
                return NOTIFY_DONE;

        poll->event = code;
        wake_up_interruptible(&poll->waitq);
        kill_fasync(&poll->fasync, SIGIO, fa_band);
        return NOTIFY_OK;
}

static void
vcs_poll_data_free(struct vcs_poll_data *poll)
{
        unregister_vt_notifier(&poll->notifier);
        kfree(poll);
}

static struct vcs_poll_data *
vcs_poll_data_get(struct file *file)
{
        struct vcs_poll_data *poll = file->private_data, *kill = NULL;

        if (poll)
                return poll;

        poll = kzalloc_obj(*poll);
        if (!poll)
                return NULL;
        poll->cons_num = console(file_inode(file));
        init_waitqueue_head(&poll->waitq);
        poll->notifier.notifier_call = vcs_notifier;
        /*
         * In order not to lose any update event, we must pretend one might
         * have occurred before we have a chance to register our notifier.
         * This is also how user space has come to detect which kernels
         * support POLLPRI on /dev/vcs* devices i.e. using poll() with
         * POLLPRI and a zero timeout.
         */
        poll->event = VT_UPDATE;

        if (register_vt_notifier(&poll->notifier) != 0) {
                kfree(poll);
                return NULL;
        }

        /*
         * This code may be called either through ->poll() or ->fasync().
         * If we have two threads using the same file descriptor, they could
         * both enter this function, both notice that the structure hasn't
         * been allocated yet and go ahead allocating it in parallel, but
         * only one of them must survive and be shared otherwise we'd leak
         * memory with a dangling notifier callback.
         */
        spin_lock(&file->f_lock);
        if (!file->private_data) {
                file->private_data = poll;
        } else {
                /* someone else raced ahead of us */
                kill = poll;
                poll = file->private_data;
        }
        spin_unlock(&file->f_lock);
        if (kill)
                vcs_poll_data_free(kill);

        return poll;
}

/**
 * vcs_vc - return VC for @inode
 * @inode: inode for which to return a VC
 * @viewed: returns whether this console is currently foreground (viewed)
 *
 * Must be called with console_lock.
 */
static struct vc_data *vcs_vc(struct inode *inode, bool *viewed)
{
        unsigned int currcons = console(inode);

        WARN_CONSOLE_UNLOCKED();

        if (currcons == 0) {
                currcons = fg_console;
                if (viewed)
                        *viewed = true;
        } else {
                currcons--;
                if (viewed)
                        *viewed = false;
        }
        return vc_cons[currcons].d;
}

/**
 * vcs_size - return size for a VC in @vc
 * @vc: which VC
 * @attr: does it use attributes?
 * @unicode: is it unicode?
 *
 * Must be called with console_lock.
 */
static int vcs_size(const struct vc_data *vc, bool attr, bool unicode)
{
        int size;

        WARN_CONSOLE_UNLOCKED();

        size = vc->vc_rows * vc->vc_cols;

        if (attr) {
                if (unicode)
                        return -EOPNOTSUPP;

                size = 2 * size + HEADER_SIZE;
        } else if (unicode)
                size *= 4;

        return size;
}

static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
{
        struct inode *inode = file_inode(file);
        struct vc_data *vc;
        int size;

        scoped_guard(console_lock) {
                vc = vcs_vc(inode, NULL);
                if (!vc)
                        return -ENXIO;

                size = vcs_size(vc, use_attributes(inode), use_unicode(inode));
        }
        if (size < 0)
                return size;
        return fixed_size_llseek(file, offset, orig, size);
}

static int vcs_read_buf_uni(struct vc_data *vc, char *con_buf,
                unsigned int pos, unsigned int count, bool viewed)
{
        unsigned int nr, row, col, maxcol = vc->vc_cols;
        int ret;

        ret = vc_uniscr_check(vc);
        if (ret)
                return ret;

        pos /= 4;
        row = pos / maxcol;
        col = pos % maxcol;
        nr = maxcol - col;
        do {
                if (nr > count / 4)
                        nr = count / 4;
                vc_uniscr_copy_line(vc, con_buf, viewed, row, col, nr);
                con_buf += nr * 4;
                count -= nr * 4;
                row++;
                col = 0;
                nr = maxcol;
        } while (count);

        return 0;
}

static void vcs_read_buf_noattr(const struct vc_data *vc, char *con_buf,
                unsigned int pos, unsigned int count, bool viewed)
{
        u16 *org;
        unsigned int col, maxcol = vc->vc_cols;

        org = screen_pos(vc, pos, viewed);
        col = pos % maxcol;
        pos += maxcol - col;

        while (count-- > 0) {
                *con_buf++ = (vcs_scr_readw(vc, org++) & 0xff);
                if (++col == maxcol) {
                        org = screen_pos(vc, pos, viewed);
                        col = 0;
                        pos += maxcol;
                }
        }
}

static unsigned int vcs_read_buf(const struct vc_data *vc, char *con_buf,
                unsigned int pos, unsigned int count, bool viewed,
                unsigned int *skip)
{
        u16 *org, *con_buf16;
        unsigned int col, maxcol = vc->vc_cols;
        unsigned int filled = count;

        if (pos < HEADER_SIZE) {
                /* clamp header values if they don't fit */
                con_buf[0] = min(vc->vc_rows, 0xFFu);
                con_buf[1] = min(vc->vc_cols, 0xFFu);
                getconsxy(vc, con_buf + 2);

                *skip += pos;
                count += pos;
                if (count > CON_BUF_SIZE) {
                        count = CON_BUF_SIZE;
                        filled = count - pos;
                }

                /* Advance state pointers and move on. */
                count -= min(HEADER_SIZE, count);
                pos = HEADER_SIZE;
                con_buf += HEADER_SIZE;
                /* If count >= 0, then pos is even... */
        } else if (pos & 1) {
                /*
                 * Skip first byte for output if start address is odd. Update
                 * region sizes up/down depending on free space in buffer.
                 */
                (*skip)++;
                if (count < CON_BUF_SIZE)
                        count++;
                else
                        filled--;
        }

        if (!count)
                return filled;

        pos -= HEADER_SIZE;
        pos /= 2;
        col = pos % maxcol;

        org = screen_pos(vc, pos, viewed);
        pos += maxcol - col;

        /*
         * Buffer has even length, so we can always copy character + attribute.
         * We do not copy last byte to userspace if count is odd.
         */
        count = (count + 1) / 2;
        con_buf16 = (u16 *)con_buf;

        while (count) {
                *con_buf16++ = vcs_scr_readw(vc, org++);
                count--;
                if (++col == maxcol) {
                        org = screen_pos(vc, pos, viewed);
                        col = 0;
                        pos += maxcol;
                }
        }

        return filled;
}

static ssize_t
vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
        struct inode *inode = file_inode(file);
        struct vc_data *vc;
        struct vcs_poll_data *poll;
        unsigned int read;
        ssize_t ret;
        loff_t pos;
        bool viewed, attr, uni_mode;

        char *con_buf __free(free_page_ptr) = (char *)__get_free_page(GFP_KERNEL);
        if (!con_buf)
                return -ENOMEM;

        pos = *ppos;

        /* Select the proper current console and verify
         * sanity of the situation under the console lock.
         */
        guard(console_lock)();

        uni_mode = use_unicode(inode);
        attr = use_attributes(inode);

        if (pos < 0)
                return -EINVAL;
        /* we enforce 32-bit alignment for pos and count in unicode mode */
        if (uni_mode && (pos | count) & 3)
                return -EINVAL;

        poll = file->private_data;
        if (count && poll)
                poll->event = 0;
        read = 0;
        ret = 0;
        while (count) {
                unsigned int this_round, skip = 0;
                int size;

                vc = vcs_vc(inode, &viewed);
                if (!vc) {
                        ret = -ENXIO;
                        break;
                }

                /* Check whether we are above size each round,
                 * as copy_to_user at the end of this loop
                 * could sleep.
                 */
                size = vcs_size(vc, attr, uni_mode);
                if (size < 0) {
                        ret = size;
                        break;
                }
                if (pos >= size)
                        break;
                if (count > size - pos)
                        count = size - pos;

                this_round = count;
                if (this_round > CON_BUF_SIZE)
                        this_round = CON_BUF_SIZE;

                /* Perform the whole read into the local con_buf.
                 * Then we can drop the console spinlock and safely
                 * attempt to move it to userspace.
                 */

                if (uni_mode) {
                        ret = vcs_read_buf_uni(vc, con_buf, pos, this_round,
                                        viewed);
                        if (ret)
                                break;
                } else if (!attr) {
                        vcs_read_buf_noattr(vc, con_buf, pos, this_round,
                                        viewed);
                } else {
                        this_round = vcs_read_buf(vc, con_buf, pos, this_round,
                                        viewed, &skip);
                }

                /* Finally, release the console semaphore while we push
                 * all the data to userspace from our temporary buffer.
                 *
                 * AKPM: Even though it's a semaphore, we should drop it because
                 * the pagefault handling code may want to call printk().
                 */

                console_unlock();
                ret = copy_to_user(buf, con_buf + skip, this_round);
                console_lock();

                if (ret) {
                        read += this_round - ret;
                        ret = -EFAULT;
                        break;
                }
                buf += this_round;
                pos += this_round;
                read += this_round;
                count -= this_round;
        }
        *ppos += read;
        if (read)
                return read;

        return ret;
}

static u16 *vcs_write_buf_noattr(struct vc_data *vc, const char *con_buf,
                unsigned int pos, unsigned int count, bool viewed, u16 **org0)
{
        u16 *org;
        unsigned int col, maxcol = vc->vc_cols;

        *org0 = org = screen_pos(vc, pos, viewed);
        col = pos % maxcol;
        pos += maxcol - col;

        while (count > 0) {
                unsigned char c = *con_buf++;

                count--;
                vcs_scr_writew(vc,
                               (vcs_scr_readw(vc, org) & 0xff00) | c, org);
                org++;
                if (++col == maxcol) {
                        org = screen_pos(vc, pos, viewed);
                        col = 0;
                        pos += maxcol;
                }
        }

        return org;
}

/*
 * Compilers (gcc 10) are unable to optimize the swap in cpu_to_le16. So do it
 * the poor man way.
 */
static inline u16 vc_compile_le16(u8 hi, u8 lo)
{
#ifdef __BIG_ENDIAN
        return (lo << 8u) | hi;
#else
        return (hi << 8u) | lo;
#endif
}

static u16 *vcs_write_buf(struct vc_data *vc, const char *con_buf,
                unsigned int pos, unsigned int count, bool viewed, u16 **org0)
{
        u16 *org;
        unsigned int col, maxcol = vc->vc_cols;
        unsigned char c;

        /* header */
        if (pos < HEADER_SIZE) {
                char header[HEADER_SIZE];

                getconsxy(vc, header + 2);
                while (pos < HEADER_SIZE && count > 0) {
                        count--;
                        header[pos++] = *con_buf++;
                }
                if (!viewed)
                        putconsxy(vc, header + 2);
        }

        if (!count)
                return NULL;

        pos -= HEADER_SIZE;
        col = (pos/2) % maxcol;

        *org0 = org = screen_pos(vc, pos/2, viewed);

        /* odd pos -- the first single character */
        if (pos & 1) {
                count--;
                c = *con_buf++;
                vcs_scr_writew(vc, vc_compile_le16(c, vcs_scr_readw(vc, org)),
                                org);
                org++;
                pos++;
                if (++col == maxcol) {
                        org = screen_pos(vc, pos/2, viewed);
                        col = 0;
                }
        }

        pos /= 2;
        pos += maxcol - col;

        /* even pos -- handle attr+character pairs */
        while (count > 1) {
                unsigned short w;

                w = get_unaligned(((unsigned short *)con_buf));
                vcs_scr_writew(vc, w, org++);
                con_buf += 2;
                count -= 2;
                if (++col == maxcol) {
                        org = screen_pos(vc, pos, viewed);
                        col = 0;
                        pos += maxcol;
                }
        }

        if (!count)
                return org;

        /* odd pos -- the remaining character */
        c = *con_buf++;
        vcs_scr_writew(vc, vc_compile_le16(vcs_scr_readw(vc, org) >> 8, c),
                                org);

        return org;
}

static ssize_t
vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
        struct inode *inode = file_inode(file);
        struct vc_data *vc;
        u16 *org0, *org;
        unsigned int written;
        int size;
        ssize_t ret;
        loff_t pos;
        bool viewed, attr;

        if (use_unicode(inode))
                return -EOPNOTSUPP;

        char *con_buf __free(free_page_ptr) = (char *)__get_free_page(GFP_KERNEL);
        if (!con_buf)
                return -ENOMEM;

        pos = *ppos;

        /* Select the proper current console and verify
         * sanity of the situation under the console lock.
         */
        guard(console_lock)();

        attr = use_attributes(inode);
        vc = vcs_vc(inode, &viewed);
        if (!vc)
                return -ENXIO;

        size = vcs_size(vc, attr, false);
        if (size < 0)
                return size;
        if (pos < 0 || pos > size)
                return -EINVAL;
        if (count > size - pos)
                count = size - pos;
        written = 0;
        while (count) {
                unsigned int this_round = count;

                if (this_round > CON_BUF_SIZE)
                        this_round = CON_BUF_SIZE;

                /* Temporarily drop the console lock so that we can read
                 * in the write data from userspace safely.
                 */
                console_unlock();
                ret = copy_from_user(con_buf, buf, this_round);
                console_lock();

                if (ret) {
                        this_round -= ret;
                        if (!this_round) {
                                /* Abort loop if no data were copied. Otherwise
                                 * fail with -EFAULT.
                                 */
                                if (written)
                                        break;
                                return -EFAULT;
                        }
                }

                /* The vc might have been freed or vcs_size might have changed
                 * while we slept to grab the user buffer, so recheck.
                 * Return data written up to now on failure.
                 */
                vc = vcs_vc(inode, &viewed);
                if (!vc) {
                        if (written)
                                break;
                        return -ENXIO;
                }
                size = vcs_size(vc, attr, false);
                if (size < 0) {
                        if (written)
                                break;
                        return size;
                }
                if (pos >= size)
                        break;
                if (this_round > size - pos)
                        this_round = size - pos;

                /* OK, now actually push the write to the console
                 * under the lock using the local kernel buffer.
                 */

                if (attr)
                        org = vcs_write_buf(vc, con_buf, pos, this_round,
                                        viewed, &org0);
                else
                        org = vcs_write_buf_noattr(vc, con_buf, pos, this_round,
                                        viewed, &org0);

                count -= this_round;
                written += this_round;
                buf += this_round;
                pos += this_round;
                if (org)
                        update_region(vc, (unsigned long)(org0), org - org0);
        }
        *ppos += written;
        ret = written;
        if (written)
                vcs_scr_updated(vc);

        return ret;
}

static __poll_t
vcs_poll(struct file *file, poll_table *wait)
{
        struct vcs_poll_data *poll = vcs_poll_data_get(file);
        __poll_t ret = DEFAULT_POLLMASK|EPOLLERR;

        if (poll) {
                poll_wait(file, &poll->waitq, wait);
                switch (poll->event) {
                case VT_UPDATE:
                        ret = DEFAULT_POLLMASK|EPOLLPRI;
                        break;
                case VT_DEALLOCATE:
                        ret = DEFAULT_POLLMASK|EPOLLHUP|EPOLLERR;
                        break;
                case 0:
                        ret = DEFAULT_POLLMASK;
                        break;
                }
        }
        return ret;
}

static int
vcs_fasync(int fd, struct file *file, int on)
{
        struct vcs_poll_data *poll = file->private_data;

        if (!poll) {
                /* don't allocate anything if all we want is disable fasync */
                if (!on)
                        return 0;
                poll = vcs_poll_data_get(file);
                if (!poll)
                        return -ENOMEM;
        }

        return fasync_helper(fd, file, on, &poll->fasync);
}

static int
vcs_open(struct inode *inode, struct file *filp)
{
        unsigned int currcons = console(inode);
        bool attr = use_attributes(inode);
        bool uni_mode = use_unicode(inode);

        /* we currently don't support attributes in unicode mode */
        if (attr && uni_mode)
                return -EOPNOTSUPP;

        guard(console_lock)();

        if (currcons && !vc_cons_allocated(currcons - 1))
                return -ENXIO;

        return 0;
}

static int vcs_release(struct inode *inode, struct file *file)
{
        struct vcs_poll_data *poll = file->private_data;

        if (poll)
                vcs_poll_data_free(poll);
        return 0;
}

static const struct file_operations vcs_fops = {
        .llseek         = vcs_lseek,
        .read           = vcs_read,
        .write          = vcs_write,
        .poll           = vcs_poll,
        .fasync         = vcs_fasync,
        .open           = vcs_open,
        .release        = vcs_release,
};

static const struct class vc_class = {
        .name = "vc",
};

void vcs_make_sysfs(int index)
{
        device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL, "vcs%u", index + 1);
        device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, index + 65), NULL, "vcsu%u", index + 1);
        device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL, "vcsa%u", index + 1);
}

void vcs_remove_sysfs(int index)
{
        device_destroy(&vc_class, MKDEV(VCS_MAJOR, index + 1));
        device_destroy(&vc_class, MKDEV(VCS_MAJOR, index + 65));
        device_destroy(&vc_class, MKDEV(VCS_MAJOR, index + 129));
}

int __init vcs_init(void)
{
        unsigned int i;

        if (register_chrdev(VCS_MAJOR, "vcs", &vcs_fops))
                panic("unable to get major %d for vcs device", VCS_MAJOR);
        if (class_register(&vc_class))
                panic("unable to create vc_class");

        device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
        device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, 64), NULL, "vcsu");
        device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
        for (i = 0; i < MIN_NR_CONSOLES; i++)
                vcs_make_sysfs(i);
        return 0;
}