From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> stable inclusion from stable-v5.10.88 commit fd623e16b2ff83ce8579f1ce11ad5f2debeabfbb bugzilla: 186058 https://gitee.com/openeuler/kernel/issues/I4QW6A Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 1ee33b1ca2b8dabfcc17198ffd049a6b55674a86 upstream. 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... Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Chen Jun <chenjun102@huawei.com> Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> --- drivers/tty/n_hdlc.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index 1363e659dc1d..48c64e68017c 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -139,6 +139,8 @@ 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; }; /* @@ -153,6 +155,7 @@ 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; @@ -209,6 +212,8 @@ 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); @@ -240,6 +245,8 @@ 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; @@ -333,6 +340,20 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty) 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 @@ -343,7 +364,7 @@ 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() */ /** -- 2.20.1