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tty: n_hdlc: make n_hdlc_tty_wakeup() asynchronous 

syzbot is reporting that an unprivileged user who logged in from tty
console can crash the system using a reproducer shown below [1], for
n_hdlc_tty_wakeup() is synchronously calling n_hdlc_send_frames().

----------
  #include <sys/ioctl.h>
  #include <unistd.h>

  int main(int argc, char *argv[])
  {
    const int disc = 0xd;

    ioctl(1, TIOCSETD, &disc);
    while (1) {
      ioctl(1, TCXONC, 0);
      write(1, "", 1);
      ioctl(1, TCXONC, 1); /* Kernel panic - not syncing: scheduling while atomic */
    }
  }
----------

Linus suspected that "struct tty_ldisc"->ops->write_wakeup() must not
sleep, and Jiri confirmed it from include/linux/tty_ldisc.h. Thus, defer
n_hdlc_send_frames() from n_hdlc_tty_wakeup() to a WQ context like
net/nfc/nci/uart.c does.

Link: https://syzkaller.appspot.com/bug?extid=5f47a8cea6a12b77a876 [1]
Reported-by: syzbot <syzbot+5f47a8cea6a12b77a876@syzkaller.appspotmail.com>
Cc: stable <stable@vger.kernel.org>
Analyzed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Confirmed-by: Jiri Slaby <jirislaby@kernel.org>
Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/40de8b7e-a3be-4486-4e33-1b1d1da452f8@i-love.sakura.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tetsuo Handa 2021-12-15 20:52:40 +09:00 committed by Greg Kroah-Hartman
parent 0fcfb00b28
commit 1ee33b1ca2
1 changed files with 22 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
drivers/tty/n_hdlc.c
View File

@ -140,6 +140,8 @@ struct n_hdlc {
struct n_hdlc_buf_list rx_buf_list;
struct n_hdlc_buf_list tx_free_buf_list;
struct n_hdlc_buf_list rx_free_buf_list;
struct work_struct write_work;
struct tty_struct *tty_for_write_work;
};
/*
@ -154,6 +156,7 @@ static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
/* Local functions */
static struct n_hdlc *n_hdlc_alloc(void);
static void n_hdlc_tty_write_work(struct work_struct *work);
/* max frame size for memory allocations */
static int maxframe = 4096;
@ -210,6 +213,8 @@ static void n_hdlc_tty_close(struct tty_struct *tty)
wake_up_interruptible(&tty->read_wait);
wake_up_interruptible(&tty->write_wait);
cancel_work_sync(&n_hdlc->write_work);
n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
@ -241,6 +246,8 @@ static int n_hdlc_tty_open(struct tty_struct *tty)
return -ENFILE;
}
INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work);
n_hdlc->tty_for_write_work = tty;
tty->disc_data = n_hdlc;
tty->receive_room = 65536;
@ -334,6 +341,20 @@ check_again:
goto check_again;
} /* end of n_hdlc_send_frames() */
/**
* n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup
* @work: pointer to work_struct
*
* Called when low level device driver can accept more send data.
*/
static void n_hdlc_tty_write_work(struct work_struct *work)
{
struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work);
struct tty_struct *tty = n_hdlc->tty_for_write_work;
n_hdlc_send_frames(n_hdlc, tty);
} /* end of n_hdlc_tty_write_work() */
/**
* n_hdlc_tty_wakeup - Callback for transmit wakeup
* @tty: pointer to associated tty instance data
@ -344,7 +365,7 @@ static void n_hdlc_tty_wakeup(struct tty_struct *tty)
{
struct n_hdlc *n_hdlc = tty->disc_data;
n_hdlc_send_frames(n_hdlc, tty);
schedule_work(&n_hdlc->write_work);
} /* end of n_hdlc_tty_wakeup() */
/**