[syzbot] [net?] WARNING: suspicious RCU usage in xfrm_nlmsg_multicast

[syzbot <syzbot+c0e99a1aa85a286d7a3b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    4235cb24ec1e Merge tag 'vfs-7.2-rc5.fixes' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=126091b9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a
dashboard link: https://syzkaller.appspot.com/bug?extid=c0e99a1aa85a286d7a3b
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16f16499580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14d5e6b9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/34e9a122d3c0/disk-4235cb24.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f5c47e8d86e0/vmlinux-4235cb24.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b287db60160f/bzImage-4235cb24.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c0e99a1aa85a286d7a3b@syzkaller.appspotmail.com

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
net/xfrm/xfrm_user.c:1630 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.0.17/5947:
 #0: ffff888029cda048 (&net->xfrm.xfrm_cfg_mutex){+.+.}-{4:4}, at: xfrm_netlink_rcv+0x6a/0x90 net/xfrm/xfrm_user.c:3928

stack backtrace:
CPU: 1 UID: 0 PID: 5947 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 lockdep_rcu_suspicious+0x13f/0x1d0 kernel/locking/lockdep.c:6876
 xfrm_nlmsg_multicast+0x1d8/0x1f0 net/xfrm/xfrm_user.c:1630
 xfrm_send_migrate_state+0x870/0xae0 net/xfrm/xfrm_user.c:3340
 xfrm_do_migrate_state+0x1749/0x1e90 net/xfrm/xfrm_user.c:3507
 xfrm_user_rcv_msg+0x7a8/0xf30 net/xfrm/xfrm_user.c:3907
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 xfrm_netlink_rcv+0x79/0x90 net/xfrm/xfrm_user.c:3929
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7f5/0x990 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0x565/0x870 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmsg net/socket.c:2770 [inline]
 __do_sys_sendmsg net/socket.c:2775 [inline]
 __se_sys_sendmsg net/socket.c:2773 [inline]
 __x64_sys_sendmsg+0x1b7/0x290 net/socket.c:2773
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb235fede99
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:00007ffc10a8b768 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fb236275fa0 RCX: 00007fb235fede99
RDX: 0000000000000000 RSI: 0000200000000500 RDI: 0000000000000003
RBP: 00007fb236083eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb236275fac R14: 00007fb236275fa0 R15: 00007fb236275fa0
 </TASK>


---
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