Patch "af_unix: Fix data-race around unix_tot_inflight." has been added to the 4.14-stable tree

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

    af_unix: Fix data-race around unix_tot_inflight.

to the 4.14-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-fix-data-race-around-unix_tot_inflight.patch
and it can be found in the queue-4.14 subdirectory.

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



commit b49b5522bdfb511a9665a890a9f6a50f123b8dba
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Fri Sep 1 17:27:06 2023 -0700

    af_unix: Fix data-race around unix_tot_inflight.
    
    [ Upstream commit ade32bd8a738d7497ffe9743c46728db26740f78 ]
    
    unix_tot_inflight is changed under spin_lock(unix_gc_lock), but
    unix_release_sock() reads it locklessly.
    
    Let's use READ_ONCE() for unix_tot_inflight.
    
    Note that the writer side was marked by commit 9d6d7f1cb67c ("af_unix:
    annote lockless accesses to unix_tot_inflight & gc_in_progress")
    
    BUG: KCSAN: data-race in unix_inflight / unix_release_sock
    
    write (marked) to 0xffffffff871852b8 of 4 bytes by task 123 on cpu 1:
     unix_inflight+0x130/0x180 net/unix/scm.c:64
     unix_attach_fds+0x137/0x1b0 net/unix/scm.c:123
     unix_scm_to_skb net/unix/af_unix.c:1832 [inline]
     unix_dgram_sendmsg+0x46a/0x14f0 net/unix/af_unix.c:1955
     sock_sendmsg_nosec net/socket.c:724 [inline]
     sock_sendmsg+0x148/0x160 net/socket.c:747
     ____sys_sendmsg+0x4e4/0x610 net/socket.c:2493
     ___sys_sendmsg+0xc6/0x140 net/socket.c:2547
     __sys_sendmsg+0x94/0x140 net/socket.c:2576
     __do_sys_sendmsg net/socket.c:2585 [inline]
     __se_sys_sendmsg net/socket.c:2583 [inline]
     __x64_sys_sendmsg+0x45/0x50 net/socket.c:2583
     do_syscall_x64 arch/x86/entry/common.c:50 [inline]
     do_syscall_64+0x3b/0x90 arch/x86/entry/common.c:80
     entry_SYSCALL_64_after_hwframe+0x72/0xdc
    
    read to 0xffffffff871852b8 of 4 bytes by task 4891 on cpu 0:
     unix_release_sock+0x608/0x910 net/unix/af_unix.c:671
     unix_release+0x59/0x80 net/unix/af_unix.c:1058
     __sock_release+0x7d/0x170 net/socket.c:653
     sock_close+0x19/0x30 net/socket.c:1385
     __fput+0x179/0x5e0 fs/file_table.c:321
     ____fput+0x15/0x20 fs/file_table.c:349
     task_work_run+0x116/0x1a0 kernel/task_work.c:179
     resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
     exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
     exit_to_user_mode_prepare+0x174/0x180 kernel/entry/common.c:204
     __syscall_exit_to_user_mode_work kernel/entry/common.c:286 [inline]
     syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:297
     do_syscall_64+0x4b/0x90 arch/x86/entry/common.c:86
     entry_SYSCALL_64_after_hwframe+0x72/0xdc
    
    value changed: 0x00000000 -> 0x00000001
    
    Reported by Kernel Concurrency Sanitizer on:
    CPU: 0 PID: 4891 Comm: systemd-coredum Not tainted 6.4.0-rc5-01219-gfa0e21fa4443 #5
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
    
    Fixes: 9305cfa4443d ("[AF_UNIX]: Make unix_tot_inflight counter non-atomic")
    Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 4def6e954e486..8d25d50f916ea 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -589,7 +589,7 @@ static void unix_release_sock(struct sock *sk, int embrion)
 	 *	  What the above comment does talk about? --ANK(980817)
 	 */
 
-	if (unix_tot_inflight)
+	if (READ_ONCE(unix_tot_inflight))
 		unix_gc();		/* Garbage collect fds */
 }
 



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