linux-kernel - Re: [syzbot] [kernel?] KASAN: slab-use-after-free Read in futex

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Message-ID: <698bbbf6.a70a0220.2c38d7.007d.GAE@google.com>
Date: Tue, 10 Feb 2026 15:15:02 -0800
From: syzbot <syzbot+6c1861115b4253e45969@...kaller.appspotmail.com>
To: hdanton@...a.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] KASAN: slab-use-after-free Read in futex_unqueue

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel BUG in __mmput

------------[ cut here ]------------
kernel BUG at kernel/fork.c:1168!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6657 Comm: syz.0.84 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:__mmput kernel/fork.c:1168 [inline]
RIP: 0010:__mmput+0x36a/0x410 kernel/fork.c:1166
Code: e8 ab 9c 41 00 48 89 df e8 43 ba b3 00 e9 c4 fd ff ff e8 99 9c 41 00 48 89 df e8 e1 b1 ab 00 e9 65 fd ff ff e8 87 9c 41 00 90 <0f> 0b e8 7f 9c 41 00 48 89 df e8 c7 cc ff ff eb b3 48 89 ef e8 bd
RSP: 0000:ffffc90003107b50 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88802a7124c0 RCX: ffffffff81c4f02d
RDX: ffff8880784e1e40 RSI: ffffffff81c4f339 RDI: ffff8880784e1e40
RBP: 00000000ffffffff R08: 0000000000000005 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000000 R12: 0000000000000200
R13: ffff88802a712790 R14: ffff88801cf9f400 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881245bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557ac0c4e8 CR3: 0000000028ca2000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 mmput+0x67/0x80 kernel/fork.c:1197
 exit_mm kernel/exit.c:581 [inline]
 do_exit+0x78a/0x2a30 kernel/exit.c:959
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1112
 get_signal+0x1ec7/0x21e0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x91/0x770 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x86/0x4a0 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x668/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f362119bf79
Code: Unable to access opcode bytes at 0x7f362119bf4f.
RSP: 002b:00007f36220860e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f3621415fa8 RCX: 00007f362119bf79
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f3621415fa8
RBP: 00007f3621415fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3621416038 R14: 00007ffc4753fb50 R15: 00007ffc4753fc38
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__mmput kernel/fork.c:1168 [inline]
RIP: 0010:__mmput+0x36a/0x410 kernel/fork.c:1166
Code: e8 ab 9c 41 00 48 89 df e8 43 ba b3 00 e9 c4 fd ff ff e8 99 9c 41 00 48 89 df e8 e1 b1 ab 00 e9 65 fd ff ff e8 87 9c 41 00 90 <0f> 0b e8 7f 9c 41 00 48 89 df e8 c7 cc ff ff eb b3 48 89 ef e8 bd
RSP: 0000:ffffc90003107b50 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88802a7124c0 RCX: ffffffff81c4f02d
RDX: ffff8880784e1e40 RSI: ffffffff81c4f339 RDI: ffff8880784e1e40
RBP: 00000000ffffffff R08: 0000000000000005 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000000 R12: 0000000000000200
R13: ffff88802a712790 R14: ffff88801cf9f400 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881245bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557ac0c4e8 CR3: 0000000075a0c000 CR4: 00000000003526f0


Tested on:

commit:         dc855b77 Merge tag 'irq-drivers-2026-02-09' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11aab402580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=86c6013ce1247095
dashboard link: https://syzkaller.appspot.com/bug?extid=6c1861115b4253e45969
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=111d0e5a580000