Subject: Re: [syzbot] [net?] possible deadlock in do_ipv6_setsockopt (4)

From: syzbot <[email-masked]>
Date: Sun, 02 Feb 2025 14:01:18 -0800

syzbot has found a reproducer for the following issue on:

HEAD commit:    c2933b2befe2 Merge tag 'net-6.14-rc1' of git://git.kernel...
git tree:       net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12a22eb0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d033b14aeef39158
dashboard link: https://syzkaller.appspot.com/bug?extid=3433b5cb8b2b70933f8d
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12896d18580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12c69724580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c7667ae12603/disk-c2933b2b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/944ca63002c1/vmlinux-c2933b2b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/30748115bf0b/bzImage-c2933b2b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

======================================================
WARNING: possible circular locking dependency detected
6.13.0-syzkaller-09685-gc2933b2befe2 #0 Not tainted
------------------------------------------------------
syz-executor323/5834 is trying to acquire lock:
ffff8880352e2cd8 (sk_lock-AF_INET6){+.+.}-{0:0}, at: do_ipv6_setsockopt+0xbf7/0x3640 net/ipv6/ipv6_sockglue.c:567

but task is already holding lock:
ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: do_ipv6_setsockopt+0x9e8/0x3640 net/ipv6/ipv6_sockglue.c:566

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (rtnl_mutex){+.+.}-{4:4}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
       smc_vlan_by_tcpsk+0x399/0x4e0 net/smc/smc_core.c:1908
       __smc_connect+0x296/0x1910 net/smc/af_smc.c:1520
       smc_connect+0x868/0xde0 net/smc/af_smc.c:1696
       __sys_connect_file net/socket.c:2040 [inline]
       __sys_connect+0x288/0x2d0 net/socket.c:2059
       __do_sys_connect net/socket.c:2065 [inline]
       __se_sys_connect net/socket.c:2062 [inline]
       __x64_sys_connect+0x7a/0x90 net/socket.c:2062
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sk_lock-AF_INET6){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3163 [inline]
       check_prevs_add kernel/locking/lockdep.c:3282 [inline]
       validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
       __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
       lock_sock_nested+0x48/0x100 net/core/sock.c:3645
       do_ipv6_setsockopt+0xbf7/0x3640 net/ipv6/ipv6_sockglue.c:567
       ipv6_setsockopt+0x5d/0x170 net/ipv6/ipv6_sockglue.c:993
       do_sock_setsockopt+0x3af/0x720 net/socket.c:2298
       __sys_setsockopt net/socket.c:2323 [inline]
       __do_sys_setsockopt net/socket.c:2329 [inline]
       __se_sys_setsockopt net/socket.c:2326 [inline]
       __x64_sys_setsockopt+0x1ee/0x280 net/socket.c:2326
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(rtnl_mutex);
                               lock(sk_lock-AF_INET6);
                               lock(rtnl_mutex);
  lock(sk_lock-AF_INET6);

 *** DEADLOCK ***

1 lock held by syz-executor323/5834:
 #0: ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: do_ipv6_setsockopt+0x9e8/0x3640 net/ipv6/ipv6_sockglue.c:566

stack backtrace:
CPU: 0 UID: 0 PID: 5834 Comm: syz-executor323 Not tainted 6.13.0-syzkaller-09685-gc2933b2befe2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2076
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2208
 check_prev_add kernel/locking/lockdep.c:3163 [inline]
 check_prevs_add kernel/locking/lockdep.c:3282 [inline]
 validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 lock_sock_nested+0x48/0x100 net/core/sock.c:3645
 do_ipv6_setsockopt+0xbf7/0x3640 net/ipv6/ipv6_sockglue.c:567
 ipv6_setsockopt+0x5d/0x170 net/ipv6/ipv6_sockglue.c:993
 do_sock_setsockopt+0x3af/0x720 net/socket.c:2298
 __sys_setsockopt net/socket.c:2323 [inline]
 __do_sys_setsockopt net/socket.c:2329 [inline]
 __se_sys_setsockopt net/socket.c:2326 [inline]
 __x64_sys_setsockopt+0x1ee/0x280 net/socket.c:2326
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5f02247369
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe9a248bd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007ffe9a248da8 RCX: 00007f5f02247369
RDX: 000000000000001b RSI: 0000000000000029 RDI: 0000000000000004
RBP: 00007f5f022ba610 R08: 0000000000000000 R09: 00007ffe9a248da8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffe9a248d98 

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