diff options
| author | Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> | 2021-12-15 20:52:40 +0900 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-12-15 21:50:39 +0100 |
| commit | 1ee33b1ca2b8dabfcc17198ffd049a6b55674a86 (patch) | |
| tree | 2ce60430e41f2151ed7e848973188e2b5e29b744 /drivers/tty | |
| parent | 0fcfb00b28c0b7884635dacf38e46d60bf3d4eb1 (diff) | |
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>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/n_hdlc.c | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index 7e0884ecc74f..23ba1fc99df8 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -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; @@ -335,6 +342,20 @@ 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() */ /** |