Messages in this thread | | | Date | Wed, 15 Jun 2022 12:47:20 +0200 | Subject | Re: CVE-2022-1462: race condition vulnerability in drivers/tty/tty_buffers.c | From | Jiri Slaby <> |
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On 02. 06. 22, 6:48, Jiri Slaby wrote: > On 02. 06. 22, 4:48, Hillf Danton wrote: >> On Wed, 1 Jun 2022 21:34:26 +0300 Dan Carpenter wrote: >>> Hi Greg, Jiri, >>> >>> I searched lore.kernel.org and it seemed like CVE-2022-1462 might not >>> have ever been reported to you? Here is the original email with the >>> syzkaller reproducer. >>> >>> https://seclists.org/oss-sec/2022/q2/155 >>> >>> The reporter proposed a fix, but it won't work. Smatch says that some >>> of the callers are already holding the port->lock. For example, >>> sci_dma_rx_complete() will deadlock. >> >> Hi Dan >> >> To erase the deadlock above, we need to add another helper folding >> tty_insert_flip_string() and tty_flip_buffer_push() into one nutshell, >> with buf->tail covered by port->lock. >> >> The diff attached in effect reverts >> 71a174b39f10 ("pty: do tty_flip_buffer_push without port->lock in >> pty_write"). >> >> Only for thoughts now. > > I think this the likely the best approach. Except few points inlined below. > > Another would be to split tty_flip_buffer_push() into two and call only > the first one (doing smp_store_release()) inside the lock. I tried that > already, but it looks much worse. > > Another would be to add flags to tty_flip_buffer_push(). Like > ONLY_ADVANCE and ONLY_QUEUE. Call with the first under the lock, the > second outside. > > Ideas, comments?
Apparently not, so Hillf, could you resend your patch after fixing the comments below?
Thanks.
>> Hillf >> >> +++ b/drivers/tty/pty.c >> @@ -116,15 +116,8 @@ static int pty_write(struct tty_struct * >> if (tty->flow.stopped) >> return 0; >> - if (c > 0) { >> - spin_lock_irqsave(&to->port->lock, flags); >> - /* Stuff the data into the input queue of the other end */ >> - c = tty_insert_flip_string(to->port, buf, c); >> - spin_unlock_irqrestore(&to->port->lock, flags); >> - /* And shovel */ >> - if (c) >> - tty_flip_buffer_push(to->port); >> - } >> + if (c > 0) >> + c = tty_flip_insert_and_push_buffer(to->port, buf, c); >> return c; >> } >> +++ b/drivers/tty/tty_buffer.c >> @@ -554,6 +554,26 @@ void tty_flip_buffer_push(struct tty_por >> } >> EXPORT_SYMBOL(tty_flip_buffer_push); >> +int tty_flip_insert_and_push_buffer(struct tty_port *port, const >> unsigned char *string, int cnt) > > It should be _insert_string_, IMO. > >> +{ >> + struct tty_bufhead *buf = &port->buf; >> + unsigned long flags; >> + >> + spin_lock_irqsave(&port->lock, flags); >> + cnt = tty_insert_flip_string(port, string, cnt); >> + if (cnt) { >> + /* >> + * Paired w/ acquire in flush_to_ldisc(); ensures >> flush_to_ldisc() sees >> + * buffer data. >> + */ >> + smp_store_release(&buf->tail->commit, buf->tail->used); >> + } >> + spin_unlock_irqrestore(&port->lock, flags); >> + queue_work(system_unbound_wq, &buf->work); > > \n here please. > >> + return cnt; >> +} >> +EXPORT_SYMBOL(tty_flip_insert_and_push_buffer); > > No need to export this, right? > > thanks,
-- js suse labs
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