[syzbot] kernel BUG in put_ucounts

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2734d6c1b1a0 Linux 5.14-rc2
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=175a9e12300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7273c75708b55890
dashboard link: https://syzkaller.appspot.com/bug?extid=6cd79f45bb8fa1c9eeae
userspace arch: i386

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6cd79f45bb8fa1c9eeae@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
kernel BUG at mm/slub.c:4255!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 17835 Comm: syz-executor.3 Not tainted 5.14.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kfree+0x635/0x650 mm/slub.c:4255
Code: 74 00 00 e9 d6 fe ff ff 48 c7 c6 88 c7 12 8b 48 89 ef e8 9e 2a ed ff 0f 0b 48 c7 c6 90 5f 14 8b 4c 89 e7 e8 8d 2a ed ff 0f 0b <0f> 0b e8 14 91 6e 07 e9 d4 fe ff ff e8 ea 90 6e 07 e9 33 56 2e 07
RSP: 0000:ffffc9000dfffbf8 EFLAGS: 00010046
RAX: ffffea00002e13c8 RBX: ffffffff8eed1130 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81345ed4 RDI: 0000000000000003
RBP: ffffea00002e13c0 R08: 000000001fffffff R09: ffffffff8b84f003
R10: ffffffff81345f19 R11: 0000000000000000 R12: ffffffff8b84f060
R13: ffff8880109ac300 R14: ffff8880925a3718 R15: ffff88806d648848
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0063) knlGS:00000000f55d2b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000050 CR3: 000000001e7fe000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 put_ucounts kernel/ucount.c:200 [inline]
 put_ucounts+0x117/0x150 kernel/ucount.c:192
 __sigqueue_free.part.0+0x9b/0xe0 kernel/signal.c:467
 __sigqueue_free kernel/signal.c:464 [inline]
 dequeue_synchronous_signal kernel/signal.c:757 [inline]
 get_signal+0xbd5/0x2160 kernel/signal.c:2688
 arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:865
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:209
 irqentry_exit_to_user_mode+0x5/0x40 kernel/entry/common.c:315
 exc_page_fault+0xc6/0x180 arch/x86/mm/fault.c:1534
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:568
RIP: 0023:0x80521e7
Code: 0c 50 e8 dc 5a 01 00 83 c4 10 85 c0 0f 84 b9 01 00 00 65 f0 83 2d d8 ff ff ff 01 8b 5c 24 08 e8 9f f7 00 00 8b 4c 24 0c 8b 00 <8b> 71 50 89 41 54 85 c0 75 05 83 fe ff 74 19 6b 44 24 1c 34 8b 4c
RSP: 002b:00000000f55d2640 EFLAGS: 00010283
RAX: 000000000000000e RBX: 0000000000000000 RCX: 0000000000000000
RDX: 00000000080521c4 RSI: 0000000000000003 RDI: 00000000080ea4f5
RBP: 000000000819afc0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 7833fd3a6afd4940 ]---
RIP: 0010:kfree+0x635/0x650 mm/slub.c:4255
Code: 74 00 00 e9 d6 fe ff ff 48 c7 c6 88 c7 12 8b 48 89 ef e8 9e 2a ed ff 0f 0b 48 c7 c6 90 5f 14 8b 4c 89 e7 e8 8d 2a ed ff 0f 0b <0f> 0b e8 14 91 6e 07 e9 d4 fe ff ff e8 ea 90 6e 07 e9 33 56 2e 07
RSP: 0000:ffffc9000dfffbf8 EFLAGS: 00010046
RAX: ffffea00002e13c8 RBX: ffffffff8eed1130 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81345ed4 RDI: 0000000000000003
RBP: ffffea00002e13c0 R08: 000000001fffffff R09: ffffffff8b84f003
R10: ffffffff81345f19 R11: 0000000000000000 R12: ffffffff8b84f060
R13: ffff8880109ac300 R14: ffff8880925a3718 R15: ffff88806d648848
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0063) knlGS:00000000f55d2b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000050 CR3: 000000001e7fe000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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