Re: [syzbot] [v9fs?] WARNING: refcount bug in p9_req_put (3)

syzbot
2024-07-22T06:14:22Z

syzbot has found a reproducer for the following issue on:

HEAD commit: 7846b618e0a4 Merge tag 'rtc-6.11' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1221eb21980000
kernel config: https://syzkaller.appspot.com/x/.config?x=be4129de17851dbe
dashboard link: https://syzkaller.appspot.com/bug?extid=d99d2414db66171fccbb
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15555ec3980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15900f49980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-7846b618.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3a2831ffe61c/vmlinux-7846b618.xz
kernel image: https://storage.googleapis.com/syzbot-assets/575e23a7c452/bzImage-7846b618.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d99d2414db66171fccbb@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 3 PID: 5213 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 3 PID: 5213 Comm: syz-executor225 Not tainted 6.10.0-syzkaller-11323-g7846b618e0a4 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 08 59 08 fd 84 db 0f 85 66 ff ff ff e8 5b 5e 08 fd c6 05 e6 c9 4e 0b 01 90 48 c7 c7 80 3b 90 8b e8 a7 9b ca fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 38 5e 08 fd 0f b6 1d c1 c9 4e 0b 31
RSP: 0018:ffffc90000908d90 EFLAGS: 00010082
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff814c9029
RDX: ffff888026a3a440 RSI: ffffffff814c9036 RDI: 0000000000000001
RBP: ffff88801e6b4ff8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff88801e6b4ff8 R14: ffff88801b0c5c00 R15: 0000000000000000
FS: 000055557f8c13c0(0000) GS:ffff88806b300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f95101d91b8 CR3: 00000000204fe000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
__refcount_sub_and_test include/linux/refcount.h:275 [inline]
__refcount_dec_and_test include/linux/refcount.h:307 [inline]
refcount_dec_and_test include/linux/refcount.h:325 [inline]
p9_req_put+0x1f4/0x250 net/9p/client.c:404
req_done+0x1e7/0x2f0 net/9p/trans_virtio.c:147
vring_interrupt drivers/virtio/virtio_ring.c:2595 [inline]
vring_interrupt+0x31b/0x400 drivers/virtio/virtio_ring.c:2570
__handle_irq_event_percpu+0x229/0x7c0 kernel/irq/handle.c:158
handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:210
handle_edge_irq+0x263/0xd10 kernel/irq/chip.c:831
generic_handle_irq_desc include/linux/irqdesc.h:173 [inline]
handle_irq arch/x86/kernel/irq.c:247 [inline]
call_irq_handler arch/x86/kernel/irq.c:259 [inline]
__common_interrupt+0xdf/0x250 arch/x86/kernel/irq.c:285
common_interrupt+0xab/0xd0 arch/x86/kernel/irq.c:278
</IRQ>
<TASK>
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:693
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x31/0x80 kernel/locking/spinlock.c:194
Code: f5 53 48 8b 74 24 10 48 89 fb 48 83 c7 18 e8 36 9d 75 f6 48 89 df e8 4e 1a 76 f6 f7 c5 00 02 00 00 75 23 9c 58 f6 c4 02 75 37 <bf> 01 00 00 00 e8 a5 90 67 f6 65 8b 05 e6 50 11 75 85 c0 74 16 5b
RSP: 0018:ffffc90003387c20 EFLAGS: 00000246
RAX: 0000000000000002 RBX: ffff88801e795280 RCX: 1ffffffff1fce401
RDX: 0000000000000000 RSI: ffffffff8b2cbac0 RDI: ffffffff8b909e40
RBP: 0000000000000246 R08: 0000000000000001 R09: 0000000000000001
R10: ffffffff8fe7645f R11: ffff88806b028a40 R12: 1ffff92000670f8c
R13: ffffffff92f07180 R14: ffff88801e794b30 R15: ffff88806b03fa18
task_rq_unlock kernel/sched/sched.h:1689 [inline]
wake_up_new_task+0x7b5/0xd30 kernel/sched/core.c:4703
kernel_clone+0x5fd/0x980 kernel/fork.c:2811
__do_sys_clone+0xba/0x100 kernel/fork.c:2923
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f95101586a3
Code: 1f 84 00 00 00 00 00 64 48 8b 04 25 10 00 00 00 45 31 c0 31 d2 31 f6 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 89 c2 85 c0 75 2c 64 48 8b 04 25 10 00 00
RSP: 002b:00007fff6f7d9978 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f95101586a3
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 0000000000000001 R08: 0000000000000000 R09: 0079746972756365
R10: 000055557f8c1690 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f95101dab60 R14: 00007f95101dcd20 R15: 00007fff6f7d9ad0
</TASK>
----------------
Code disassembly (best guess):
0: f5 cmc
1: 53 push %rbx
2: 48 8b 74 24 10 mov 0x10(%rsp),%rsi
7: 48 89 fb mov %rdi,%rbx
a: 48 83 c7 18 add $0x18,%rdi
e: e8 36 9d 75 f6 call 0xf6759d49
13: 48 89 df mov %rbx,%rdi
16: e8 4e 1a 76 f6 call 0xf6761a69
1b: f7 c5 00 02 00 00 test $0x200,%ebp
21: 75 23 jne 0x46
23: 9c pushf
24: 58 pop %rax
25: f6 c4 02 test $0x2,%ah
28: 75 37 jne 0x61
* 2a: bf 01 00 00 00 mov $0x1,%edi <-- trapping instruction
2f: e8 a5 90 67 f6 call 0xf66790d9
34: 65 8b 05 e6 50 11 75 mov %gs:0x751150e6(%rip),%eax # 0x75115121
3b: 85 c0 test %eax,%eax
3d: 74 16 je 0x55
3f: 5b pop %rbx

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