linux-kernel - Re: [syzbot] [net?] KASAN: slab-use-after-free Write in __xfrm_state

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Message-ID: <68aec02a.a70a0220.3cafd4.0016.GAE@google.com>
Date: Wed, 27 Aug 2025 01:22:02 -0700
From: syzbot <syzbot+a25ee9d20d31e483ba7b@...kaller.appspotmail.com>
To: hdanton@...a.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] KASAN: slab-use-after-free Write in __xfrm_state_delete

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: refcount bug in __xfrm_state_delete

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 24 at lib/refcount.c:28 refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Modules linked in:
CPU: 1 UID: 0 PID: 24 Comm: kworker/1:0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: events xfrm_state_gc_task
RIP: 0010:refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Code: 80 b1 e2 8b e8 77 4e bb fc 90 0f 0b 90 90 eb d7 e8 6b af f7 fc c6 05 81 7b c5 0a 01 90 48 c7 c7 e0 b1 e2 8b e8 57 4e bb fc 90 <0f> 0b 90 90 eb b7 e8 4b af f7 fc c6 05 5e 7b c5 0a 01 90 48 c7 c7
RSP: 0018:ffffc900001e7888 EFLAGS: 00010246
RAX: 516864998ccbad00 RBX: 0000000000000003 RCX: ffff88801d680000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 0000000000000000 R08: ffffc900001e75a7 R09: 1ffff9200003ceb4
R10: dffffc0000000000 R11: fffff5200003ceb5 R12: dffffc0000000000
R13: ffff88802f119aa0 R14: ffff88802f1199e8 R15: ffff88802f119b90
FS:  0000000000000000(0000) GS:ffff888125d1a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055809cc3f950 CR3: 000000007eb98000 CR4: 00000000003526f0
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]
 xfrm_state_put include/net/xfrm.h:928 [inline]
 __xfrm_state_delete+0xc73/0xde0 net/xfrm/xfrm_state.c:850
 xfrm_state_delete net/xfrm/xfrm_state.c:863 [inline]
 xfrm_state_gc_destroy net/xfrm/xfrm_state.c:618 [inline]
 xfrm_state_gc_task+0x532/0x6d0 net/xfrm/xfrm_state.c:635
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
 kthread+0x70e/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         24204116 Merge branch 'ipv6-sr-simplify-and-optimize-h..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13749462580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=67b99ceb67d33475
dashboard link: https://syzkaller.appspot.com/bug?extid=a25ee9d20d31e483ba7b
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11c49462580000