Subject: [syzbot] [net?] WARNING: refcount bug in sk_common_release (2)

From: syzbot <[email-masked]>
Date: Thu, 23 Apr 2026 06:23:32 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    2a4c0c11c019 Merge tag 's390-7.1-1' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=142dff16580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3e19fa1907a3dfda
dashboard link: https://syzkaller.appspot.com/bug?extid=8c9eede336e3a843750e
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-2a4c0c11.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2702dddfd186/vmlinux-2a4c0c11.xz
kernel image: https://storage.googleapis.com/syzbot-assets/51878be8732c/bzImage-2a4c0c11.xz

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

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28, CPU#1: syz.8.4131/20639
Modules linked in:
CPU: 1 UID: 0 PID: 20639 Comm: syz.8.4131 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28
Code: cc e8 60 a7 0f fd 48 8d 3d 99 d0 ec 0b 67 48 0f b9 3a e8 4f a7 0f fd 5b 5d e9 48 27 a4 06 e8 43 a7 0f fd 48 8d 3d 8c d0 ec 0b <67> 48 0f b9 3a e8 32 a7 0f fd 5b 5d c3 cc cc cc cc e8 26 a7 0f fd
RSP: 0018:ffffc90003aaf120 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff8880368a2280 RCX: ffffffff84f9d30b
RDX: ffff888061e04a00 RSI: ffffffff84f9d39d RDI: ffffffff90e6a430
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000000 R12: ffff8880368a2280
R13: ffffffff8a0c6f20 R14: 0000000000000000 R15: 0000000000000018
FS:  00007fd377c686c0(0000) GS:ffff8880d63db000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33023ffc CR3: 00000000308a1000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:400 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 sock_put include/net/sock.h:2009 [inline]
 sk_common_release+0x260/0x370 net/core/sock.c:4024
 inet_release+0xed/0x200 net/ipv4/af_inet.c:442
 __sock_release net/socket.c:722 [inline]
 sock_release+0x91/0x1c0 net/socket.c:750
 rxe_release_udp_tunnel drivers/infiniband/sw/rxe/rxe_net.c:294 [inline]
 rxe_sock_put+0xae/0x130 drivers/infiniband/sw/rxe/rxe_net.c:639
 rxe_net_del+0x83/0x120 drivers/infiniband/sw/rxe/rxe_net.c:660
 rxe_dellink+0x15/0x20 drivers/infiniband/sw/rxe/rxe.c:254
 nldev_dellink+0x289/0x3c0 drivers/infiniband/core/nldev.c:1849
 rdma_nl_rcv_msg+0x392/0x6f0 drivers/infiniband/core/netlink.c:195
 rdma_nl_rcv_skb.constprop.0.isra.0+0x2cb/0x410 drivers/infiniband/core/netlink.c:239
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0x9e1/0xb70 net/socket.c:2698
 ___sys_sendmsg+0x190/0x1e0 net/socket.c:2752
 __sys_sendmsg+0x170/0x220 net/socket.c:2784
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd376d9c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd377c68028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fd377016090 RCX: 00007fd376d9c819
RDX: 0000000000000004 RSI: 0000200000004680 RDI: 0000000000000003
RBP: 00007fd376e32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd377016128 R14: 00007fd377016090 R15: 00007ffe66f5e6c8
 </TASK>
----------------
Code disassembly (best guess):
   0:	cc                   	int3
   1:	e8 60 a7 0f fd       	call   0xfd0fa766
   6:	48 8d 3d 99 d0 ec 0b 	lea    0xbecd099(%rip),%rdi        # 0xbecd0a6
   d:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  12:	e8 4f a7 0f fd       	call   0xfd0fa766
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 48 27 a4 06       	jmp    0x6a42766
  1e:	e8 43 a7 0f fd       	call   0xfd0fa766
  23:	48 8d 3d 8c d0 ec 0b 	lea    0xbecd08c(%rip),%rdi        # 0xbecd0b6
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	e8 32 a7 0f fd       	call   0xfd0fa766
  34:	5b                   	pop    %rbx
  35:	5d                   	pop    %rbp
  36:	c3                   	ret
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	e8 26 a7 0f fd       	call   0xfd0fa766

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