Re: tty: tty_open can return to userspace holding tty_mutex

[Sukadev Bhattiprolu]

Eric Paris [eparis@xxxxxxxxxx] wrote:
| __tty_open could return (to userspace) holding the tty_mutex thanks to a
| regression introduced by 4a2b5fddd53b80efcb3266ee36e23b8de28e761a.  This was
| found by bisecting an fsfuzzer problem.  Admittedly I have no idea how it
| managed to tickle this 100% reliably, but it is clearly a regression and
| when hit leaves the box in a completely unusable state.  This patch lets
| the fsfuzzer test complete every time.

Good catch.


|     
| Signed-off-by: Eric Paris <eparis@xxxxxxxxxx>

Acked-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>

| 
| ---
|  drivers/char/tty_io.c |    4 +++-
|  1 files changed, 3 insertions(+), 1 deletions(-)
| 
| diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
| index d33e5ab..bc84e12 100644
| --- a/drivers/char/tty_io.c
| +++ b/drivers/char/tty_io.c
| @@ -1817,8 +1817,10 @@ got_driver:
|  		/* check whether we're reopening an existing tty */
|  		tty = tty_driver_lookup_tty(driver, inode, index);
| 
| -		if (IS_ERR(tty))
| +		if (IS_ERR(tty)) {
| +			mutex_unlock(&tty_mutex);
|  			return PTR_ERR(tty);
| +		}
|  	}
| 
|  	if (tty) {
| 
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