[PATCH] rose: Fix use-after-free in rose_timer_expiry

[Deepanshu Kartikey <kartikey406@gmail.com>]

A use-after-free bug can occur when rose_timer_expiry() in state
ROSE_STATE_2 releases the rose_neigh structure via rose_neigh_put(),
while the neighbour's timers (ftimer and t0timer) are still active
or being processed.

The race occurs between:
1. rose_timer_expiry() freeing rose_neigh via rose_neigh_put()
2. rose_t0timer_expiry() attempting to rearm itself via
   rose_start_t0timer(), which calls add_timer() on the freed
   structure

This leads to a KASAN use-after-free report when the timer code
attempts to access the freed memory:

BUG: KASAN: slab-use-after-free in timer_is_static_object+0x80/0x90
Read of size 8 at addr ffff88807e5e8498 by task syz.4.6813/32052

The buggy address is located 152 bytes inside of freed 512-byte
region allocated by rose_add_node().

Fix this by calling timer_shutdown() on both ftimer and t0timer
before releasing the rose_neigh structure. timer_shutdown() ensures
the timers are stopped and prevents them from being rearmed, even
if their callbacks are currently executing.

This fix is based on code analysis as no C reproducer is available
for this issue.

Reported-by: syzbot+62360d745376b40120b5@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 net/rose/rose_timer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/rose/rose_timer.c b/net/rose/rose_timer.c
index bb60a1654d61..6e6483c024fa 100644
--- a/net/rose/rose_timer.c
+++ b/net/rose/rose_timer.c
@@ -180,6 +180,8 @@ static void rose_timer_expiry(struct timer_list *t)
 		break;
 
 	case ROSE_STATE_2:	/* T3 */
+		timer_shutdown(&rose->neighbour->ftimer);
+		timer_shutdown(&rose->neighbour->t0timer);
 		rose_neigh_put(rose->neighbour);
 		rose_disconnect(sk, ETIMEDOUT, -1, -1);
 		break;
-- 
2.43.0