[PATCH 4.4 64/86] TTY: n_gsm, fix false positive WARN_ON

From: Greg Kroah-Hartman
Date: Mon May 30 2016 - 16:59:07 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Jiri Slaby <jslaby@xxxxxxx>

commit d175feca89a1c162f60f4e3560ca7bc9437c65eb upstream.

Dmitry reported, that the current cleanup code in n_gsm can trigger a
WARNING: CPU: 2 PID: 24238 at drivers/tty/n_gsm.c:2048 gsm_cleanup_mux+0x166/0x6b0()
Call Trace:
[<ffffffff81247ab9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:490
[<ffffffff828d0456>] gsm_cleanup_mux+0x166/0x6b0 drivers/tty/n_gsm.c:2048
[<ffffffff828d4d87>] gsmld_open+0x5b7/0x7a0 drivers/tty/n_gsm.c:2386
[<ffffffff828b9078>] tty_ldisc_open.isra.2+0x78/0xd0 drivers/tty/tty_ldisc.c:447
[<ffffffff828b973a>] tty_set_ldisc+0x1ca/0xa70 drivers/tty/tty_ldisc.c:567
[< inline >] tiocsetd drivers/tty/tty_io.c:2650
[<ffffffff828a14ea>] tty_ioctl+0xb2a/0x2140 drivers/tty/tty_io.c:2883

But this is a legal path when open fails to find a space in the
gsm_mux array and tries to clean up. So make it a standard test
instead of a warning.

Reported-by: "Dmitry Vyukov" <dvyukov@xxxxxxxxxx>
Cc: Alan Cox <alan@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/CACT4Y+bHQbAB68VFi7Romcs-Z9ZW3kQRvcq+BvHH1oa5NcAdLA@xxxxxxxxxxxxxx
Fixes: 5a640967 ("tty/n_gsm.c: fix a memory leak in gsmld_open()")
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/tty/n_gsm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2045,7 +2045,9 @@ static void gsm_cleanup_mux(struct gsm_m
- WARN_ON(i == MAX_MUX);
+ /* open failed before registering => nothing to do */
+ if (i == MAX_MUX)
+ return;

/* In theory disconnecting DLCI 0 is sufficient but for some
modems this is apparently not the case. */