Patch "af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC." has been added to the 5.15-stable tree

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This is a note to let you know that I've just added the patch titled

    af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     af_unix-call-kfree_skb-for-dead-unix_-sk-oob_skb-in-.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e34a62a71eafd14c4a00705f651d7a2f21e98a96
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Sat Feb 3 10:31:49 2024 -0800

    af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.
    
    [ Upstream commit 1279f9d9dec2d7462823a18c29ad61359e0a007d ]
    
    syzbot reported a warning [0] in __unix_gc() with a repro, which
    creates a socketpair and sends one socket's fd to itself using the
    peer.
    
      socketpair(AF_UNIX, SOCK_STREAM, 0, [3, 4]) = 0
      sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\360", iov_len=1}],
              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET,
                                          cmsg_type=SCM_RIGHTS, cmsg_data=[3]}],
              msg_controllen=24, msg_flags=0}, MSG_OOB|MSG_PROBE|MSG_DONTWAIT|MSG_ZEROCOPY) = 1
    
    This forms a self-cyclic reference that GC should finally untangle
    but does not due to lack of MSG_OOB handling, resulting in memory
    leak.
    
    Recently, commit 11498715f266 ("af_unix: Remove io_uring code for
    GC.") removed io_uring's dead code in GC and revealed the problem.
    
    The code was executed at the final stage of GC and unconditionally
    moved all GC candidates from gc_candidates to gc_inflight_list.
    That papered over the reported problem by always making the following
    WARN_ON_ONCE(!list_empty(&gc_candidates)) false.
    
    The problem has been there since commit 2aab4b969002 ("af_unix: fix
    struct pid leaks in OOB support") added full scm support for MSG_OOB
    while fixing another bug.
    
    To fix this problem, we must call kfree_skb() for unix_sk(sk)->oob_skb
    if the socket still exists in gc_candidates after purging collected skb.
    
    Then, we need to set NULL to oob_skb before calling kfree_skb() because
    it calls last fput() and triggers unix_release_sock(), where we call
    duplicate kfree_skb(u->oob_skb) if not NULL.
    
    Note that the leaked socket remained being linked to a global list, so
    kmemleak also could not detect it.  We need to check /proc/net/protocol
    to notice the unfreed socket.
    
    [0]:
    WARNING: CPU: 0 PID: 2863 at net/unix/garbage.c:345 __unix_gc+0xc74/0xe80 net/unix/garbage.c:345
    Modules linked in:
    CPU: 0 PID: 2863 Comm: kworker/u4:11 Not tainted 6.8.0-rc1-syzkaller-00583-g1701940b1a02 #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
    Workqueue: events_unbound __unix_gc
    RIP: 0010:__unix_gc+0xc74/0xe80 net/unix/garbage.c:345
    Code: 8b 5c 24 50 e9 86 f8 ff ff e8 f8 e4 22 f8 31 d2 48 c7 c6 30 6a 69 89 4c 89 ef e8 97 ef ff ff e9 80 f9 ff ff e8 dd e4 22 f8 90 <0f> 0b 90 e9 7b fd ff ff 48 89 df e8 5c e7 7c f8 e9 d3 f8 ff ff e8
    RSP: 0018:ffffc9000b03fba0 EFLAGS: 00010293
    RAX: 0000000000000000 RBX: ffffc9000b03fc10 RCX: ffffffff816c493e
    RDX: ffff88802c02d940 RSI: ffffffff896982f3 RDI: ffffc9000b03fb30
    RBP: ffffc9000b03fce0 R08: 0000000000000001 R09: fffff52001607f66
    R10: 0000000000000003 R11: 0000000000000002 R12: dffffc0000000000
    R13: ffffc9000b03fc10 R14: ffffc9000b03fc10 R15: 0000000000000001
    FS:  0000000000000000(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00005559c8677a60 CR3: 000000000d57a000 CR4: 00000000003506f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     <TASK>
     process_one_work+0x889/0x15e0 kernel/workqueue.c:2633
     process_scheduled_works kernel/workqueue.c:2706 [inline]
     worker_thread+0x8b9/0x12a0 kernel/workqueue.c:2787
     kthread+0x2c6/0x3b0 kernel/kthread.c:388
     ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
     ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
     </TASK>
    
    Reported-by: syzbot+fa3ef895554bdbfd1183@xxxxxxxxxxxxxxxxxxxxxxxxx
    Closes: https://syzkaller.appspot.com/bug?extid=fa3ef895554bdbfd1183
    Fixes: 2aab4b969002 ("af_unix: fix struct pid leaks in OOB support")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240203183149.63573-1-kuniyu@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index dc2763540393..767b338a7a2d 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -314,6 +314,17 @@ void unix_gc(void)
 	/* Here we are. Hitlist is filled. Die. */
 	__skb_queue_purge(&hitlist);
 
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+	list_for_each_entry_safe(u, next, &gc_candidates, link) {
+		struct sk_buff *skb = u->oob_skb;
+
+		if (skb) {
+			u->oob_skb = NULL;
+			kfree_skb(skb);
+		}
+	}
+#endif
+
 	spin_lock(&unix_gc_lock);
 
 	/* There could be io_uring registered files, just push them back to




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