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

[syzbot <syzbot+6c1861115b4253e45969@syzkaller.appspotmail.com>]

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:1195!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 6521 Comm: syz.0.17 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:1195 [inline]
RIP: 0010:mmput+0xd0/0xe0 kernel/fork.c:1192
Code: 5b 5d 41 5c e9 01 65 b6 09 e8 9c 9b 41 00 48 89 df e8 24 fb ff ff e8 8f 9b 41 00 5b 5d 41 5c c3 cc cc cc cc e8 81 9b 41 00 90 <0f> 0b 48 89 ef e8 c6 06 ac 00 eb 84 0f 1f 40 00 90 90 90 90 90 90
RSP: 0018:ffffc90003467b78 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888033d6d5c0 RCX: ffffffff81c4f461
RDX: ffff888026543c80 RSI: ffffffff81c4f4bf RDI: ffff888026543c80
RBP: ffff888033d6d684 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888033d6d890 R14: ffff88802b22c140 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881246bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f31e5ce6286 CR3: 00000000580b6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 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: 0033:0x7f532639bf79
Code: Unable to access opcode bytes at 0x7f532639bf4f.
RSP: 002b:00007f53271780e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00007f5326615fa8 RCX: 00007f532639bf79
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f5326615fac
RBP: 00007f5326615fa0 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5326616038 R14: 00007ffe73e55530 R15: 00007ffe73e55618
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:mmput kernel/fork.c:1195 [inline]
RIP: 0010:mmput+0xd0/0xe0 kernel/fork.c:1192
Code: 5b 5d 41 5c e9 01 65 b6 09 e8 9c 9b 41 00 48 89 df e8 24 fb ff ff e8 8f 9b 41 00 5b 5d 41 5c c3 cc cc cc cc e8 81 9b 41 00 90 <0f> 0b 48 89 ef e8 c6 06 ac 00 eb 84 0f 1f 40 00 90 90 90 90 90 90
RSP: 0018:ffffc90003467b78 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888033d6d5c0 RCX: ffffffff81c4f461
RDX: ffff888026543c80 RSI: ffffffff81c4f4bf RDI: ffff888026543c80
RBP: ffff888033d6d684 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888033d6d890 R14: ffff88802b22c140 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881246bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f31e5ce6286 CR3: 000000000e396000 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=12ad57fa580000
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=16c2365a580000