netdev - [PATCH wireless-next] wifi: mac80211: fix use-after-free risk in sta debugfs removal

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Message-ID: <20250724071555.442634-2-moonhee.lee.ca@gmail.com>
Date: Thu, 24 Jul 2025 00:15:56 -0700
From: Moon Hee Lee <moonhee.lee.ca@...il.com>
To: johannes@...solutions.net
Cc: linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev,
	netdev@...r.kernel.org,
	syzkaller-bugs@...glegroups.com,
	syzbot+d6ccd49ae046542a0641@...kaller.appspotmail.com,
	skhan@...uxfoundation.org,
	david.hunter.linux@...il.com,
	Moon Hee Lee <moonhee.lee.ca@...il.com>
Subject: [PATCH wireless-next] wifi: mac80211: fix use-after-free risk in sta debugfs removal

A NULL pointer dereference may occur in ieee80211_sta_debugfs_remove()
when debugfs_remove_recursive() is called on a dentry whose inode has
already been freed. This can happen due to a race between STA teardown
and debugfs cleanup.

Fix this by checking that both sta->debugfs_dir and its d_inode are
valid before invoking debugfs_remove_recursive().

This avoids the crash reported in syzbot bug:

  wlan1: send auth to aa:09:b7:99:c0:d7 (try 2/3)
  wlan1: send auth to aa:09:b7:99:c0:d7 (try 3/3)
  wlan1: authentication with aa:09:b7:99:c0:d7 timed out
  Oops: general protection fault, probably for non-canonical address 0xdffffc0000000029: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000148-0x000000000000014f]
  CPU: 0 UID: 0 PID: 171 Comm: kworker/u4:4 Not tainted 6.16.0-rc7-syzkaller #0 PREEMPT(full)
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
  Workqueue: events_unbound cfg80211_wiphy_work
  RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:199
  Code: 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f   92 c0 c3 cc cc cc cc cc 66 66 66 66 66 66 2e
  RSP: 0018:ffffc90001977400 EFLAGS: 00010202
  RAX: dffffc0000000000 RBX: ffffffff8b713286 RCX: ca5c1933e35f3700
  RDX: 0000000000000000 RSI: ffffffff8b713286 RDI: 0000000000000029
  RBP: ffffffff824067f0 R08: 0000000000000001 R09: 0000000000000000
  R10: dffffc0000000000 R11: ffffed10085cf24c R12: 0000000000000000
  R13: 0000000000000148 R14: 0000000000000148 R15: 0000000000000001
  FS:  0000000000000000(0000) GS:ffff88808d218000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000001b2f55ffff CR3: 000000005030a000 CR4: 0000000000352ef0
  Call Trace:
   <TASK>
   __kasan_check_byte+0x12/0x40 mm/kasan/common.c:556
   kasan_check_byte include/linux/kasan.h:399 [inline]
   lock_acquire+0x8d/0x360 kernel/locking/lockdep.c:5845
   down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
   inode_lock include/linux/fs.h:869 [inline]
   simple_recursive_removal+0x90/0x690 fs/libfs.c:616
   debugfs_remove+0x5b/0x70 fs/debugfs/inode.c:805
   ieee80211_sta_debugfs_remove+0x40/0x70 net/mac80211/debugfs_sta.c:1279
   __sta_info_destroy_part2+0x352/0x450 net/mac80211/sta_info.c:1501
   __sta_info_destroy net/mac80211/sta_info.c:1517 [inline]
   sta_info_destroy_addr+0xf5/0x140 net/mac80211/sta_info.c:1529
   ieee80211_destroy_auth_data+0x12d/0x260 net/mac80211/mlme.c:4597
   ieee80211_sta_work+0x11cf/0x3600 net/mac80211/mlme.c:8310
   cfg80211_wiphy_work+0x2df/0x460 net/wireless/core.c:435
   process_one_work kernel/workqueue.c:3238 [inline]
   process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
   worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
   kthread+0x70e/0x8a0 kernel/kthread.c:464
   ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
   </TASK>

Reported-by: syzbot+d6ccd49ae046542a0641@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d6ccd49ae046542a0641
Fixes: fc4a25c5b741 ("mac80211: remove sta_info debugfs sub-struct")
Tested-by: syzbot+d6ccd49ae046542a0641@...kaller.appspotmail.com
Signed-off-by: Moon Hee Lee <moonhee.lee.ca@...il.com>
---
 net/mac80211/debugfs_sta.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
index 49061bd4151b..912b69abab52 100644
--- a/net/mac80211/debugfs_sta.c
+++ b/net/mac80211/debugfs_sta.c
@@ -1276,7 +1276,8 @@ void ieee80211_sta_debugfs_add(struct sta_info *sta)
 
 void ieee80211_sta_debugfs_remove(struct sta_info *sta)
 {
-	debugfs_remove_recursive(sta->debugfs_dir);
+	if (sta->debugfs_dir && sta->debugfs_dir->d_inode)
+		debugfs_remove_recursive(sta->debugfs_dir);
 	sta->debugfs_dir = NULL;
 }
 
-- 
2.43.0