syzbot


WARNING: refcount bug in mpoad_close

Status: upstream: reported on 2026/03/16 08:09
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+5ec223ccb83b24ef982f@syzkaller.appspotmail.com
First crash: 42d, last: 8d07h
Discussions (3)
Title Replies (including bot) Last reply
[PATCH net v2] atm: mpoa: keep mpc->dev referenced across mpoad restart 3 (3) 2026/04/15 03:22
[PATCH net] atm: mpoa: fix mpc->dev refcount across mpoad restart 2 (2) 2026/04/10 14:03
[syzbot] [net?] WARNING: refcount bug in mpoad_close 0 (1) 2026/03/16 08:09

Sample crash report:
------------[ cut here ]------------
refcount_t: decrement hit 0; leaking memory.
WARNING: lib/refcount.c:31 at refcount_warn_saturate+0x70/0x110 lib/refcount.c:31, CPU#1: syz.1.15513/21151
Modules linked in:
CPU: 1 UID: 0 PID: 21151 Comm: syz.1.15513 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:refcount_warn_saturate+0x70/0x110 lib/refcount.c:31
Code: c6 40 33 f0 8e e8 a0 56 16 fd 83 fb 01 7e 22 83 fb 02 74 39 83 fb 03 74 47 83 fb 04 75 68 e8 07 51 16 fd 48 8d 3d 50 2b 6d 0b <67> 48 0f b9 3a eb 66 85 db 74 3e 83 fb 01 75 4c e8 eb 50 16 fd 48
RSP: 0018:ffffc90004ef7b48 EFLAGS: 00010283
RAX: ffffffff84af63c9 RBX: 0000000000000004 RCX: 0000000000080000
RDX: ffffc90011451000 RSI: 0000000000000037 RDI: ffffffff901c8f20
RBP: ffffc90004ef7ca0 R08: ffff88802d681e80 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000002 R12: f8f8f8f8f8f8f8f8
R13: dffffc0000000000 R14: ffff88805a7a0668 R15: 0000000000000001
FS:  00007f7c7da6e6c0(0000) GS:ffff888125557000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7c7da6dff8 CR3: 000000009b202000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_dec include/linux/refcount.h:461 [inline]
 refcount_dec include/linux/refcount.h:476 [inline]
 ref_tracker_free+0x6fc/0x840 lib/ref_tracker.c:298
 netdev_tracker_free include/linux/netdevice.h:4456 [inline]
 netdev_put include/linux/netdevice.h:4473 [inline]
 dev_put include/linux/netdevice.h:4499 [inline]
 mpoad_close+0x1fc/0x3e0 net/atm/mpc.c:889
 vcc_destroy_socket net/atm/common.c:181 [inline]
 vcc_release+0x10f/0x580 net/atm/common.c:205
 __sock_release net/socket.c:662 [inline]
 sock_close+0xc3/0x240 net/socket.c:1455
 __fput+0x44f/0xa70 fs/file_table.c:469
 fput_close_sync+0x11f/0x240 fs/file_table.c:574
 __do_sys_close fs/open.c:1509 [inline]
 __se_sys_close fs/open.c:1494 [inline]
 __x64_sys_close+0x7e/0x110 fs/open.c:1494
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7c7cb9c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7c7da6e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 00007f7c7ce16180 RCX: 00007f7c7cb9c819
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007f7c7cc32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7c7ce16218 R14: 00007f7c7ce16180 R15: 00007ffc6b865318
 </TASK>
----------------
Code disassembly (best guess):
   0:	c6 40 33 f0          	movb   $0xf0,0x33(%rax)
   4:	8e e8                	mov    %eax,%gs
   6:	a0 56 16 fd 83 fb 01 	movabs 0x227e01fb83fd1656,%al
   d:	7e 22
   f:	83 fb 02             	cmp    $0x2,%ebx
  12:	74 39                	je     0x4d
  14:	83 fb 03             	cmp    $0x3,%ebx
  17:	74 47                	je     0x60
  19:	83 fb 04             	cmp    $0x4,%ebx
  1c:	75 68                	jne    0x86
  1e:	e8 07 51 16 fd       	call   0xfd16512a
  23:	48 8d 3d 50 2b 6d 0b 	lea    0xb6d2b50(%rip),%rdi        # 0xb6d2b7a
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 66                	jmp    0x97
  31:	85 db                	test   %ebx,%ebx
  33:	74 3e                	je     0x73
  35:	83 fb 01             	cmp    $0x1,%ebx
  38:	75 4c                	jne    0x86
  3a:	e8 eb 50 16 fd       	call   0xfd16512a
  3f:	48                   	rex.W

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/03 04:40 net 51f4e090b9f8 4440e7c2 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING: refcount bug in mpoad_close
2026/04/03 01:54 net 70f73562d278 8b15d4ae .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING: refcount bug in mpoad_close
2026/04/15 03:52 net-next 35c2c39832e5 e2e976a8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING: refcount bug in mpoad_close
2026/03/12 06:53 net-next 17edc4e820bf 2d88ab01 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING: refcount bug in mpoad_close
2026/04/02 19:37 linux-next cc13002a9f98 8b15d4ae .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: refcount bug in mpoad_close
* Struck through repros no longer work on HEAD.