syzbot


WARNING: refcount bug in __inet_csk_reqsk_queue_drop

Status: upstream: reported on 2026/05/30 05:55
Subsystems: net
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+e809069bc15f26300526@syzkaller.appspotmail.com
First crash: 199d, last: 4d20h
✨ AI Jobs (5)
ID Workflow Result Correct Bug Created Started Finished Revision Error
35b41830-0cd3-4d89-81b5-d82aaa0f9206 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ❌ RemoteTrigger: ✅ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ WARNING: refcount bug in __inet_csk_reqsk_queue_drop 2026/05/30 12:40 2026/05/30 12:40 2026/05/30 13:37 6b4a844333e83556da95d61d7f207e7ef5cd4bc6
55f8b41e-b9fa-4b02-b4fe-599d8333cdc8 assessment-security 💥 WARNING: refcount bug in __inet_csk_reqsk_queue_drop 2026/05/14 10:12 2026/05/14 10:12 2026/05/14 10:13 6ccb967e465e832a7bfd7a116ad00d52a0923a5d failed to run ["git" "pull" "origin" "HEAD" "--depth=1" "--allow-unrelated-histories"]: exit status 128 From /app/workdir/repo/linux * branch HEAD -> FETCH_HEAD Updating files: 27% (26110/93697) Updating files: 28% (26236/93697) Updating files: 29% (27173/93697) Updating files: 30% (28110/93697) Updating files: 31% (29047/93697) Updating files: 32% (29984/93697) Updating files: 33% (30921/93697) Updating files: 34% (31857/93697) Updating files: 35% (32794/93697) Updating files: 36% (33731/93697) Updating files: 36% (34163/93697) Updating files: 37% (34668/93697) Updating files: 38% (35605/93697) Updating files: 39% (36542/93697) Updating files: 39% (37243/93697) Updating files: 39% (37353/93697) error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_11_0_0_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_11_0_3_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_11_0_3_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_11_5_0_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_11_5_0_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_12_0_0_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_12_0_0_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_12_1_0_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_12_1_0_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_0_default.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_0_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_0_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_1_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_1_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_2_1_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_2_1_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_4_1_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_4_1_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_4_2_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_4_2_sh_mask.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_4_3_offset.h error: unable to write file drivers/gpu/drm/amd/include/asic_reg/gc/gc_9_4_3_sh_mask.h fatal: cannot create directory at 'drivers/gpu/drm/amd/include/asic_reg/gca': No space left on device
2ee7a339-fb22-403a-8ae1-b36899fc0e3a repro 💥 WARNING: refcount bug in __inet_csk_reqsk_queue_drop 2026/03/27 12:52 2026/03/27 12:52 2026/03/27 12:53 911b9cd2ff48815a822e9767728aa015c33a892a failed to parse '-threaded': error splitting options token -threaded
ed8ab7cd-4abe-42a7-a1da-ed1fd73ad9d0 repro 💥 WARNING: refcount bug in __inet_csk_reqsk_queue_drop 2026/03/27 12:01 2026/03/27 12:01 2026/03/27 12:52 911b9cd2ff48815a822e9767728aa015c33a892a failed to parse '-threaded': error splitting options token -threaded
98e88454-1b9d-4537-b290-d4a0b7dbfec9 repro WARNING: refcount bug in __inet_csk_reqsk_queue_drop 2026/03/06 10:25 2026/03/06 10:25 2026/03/06 10:28 31e9c887f7dc24e04b3ca70d0d54fc34141844b0
Discussions (3)
Title Replies (including bot) Last reply
[PATCH v2 net] tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). 2 (2) 2026/06/01 18:46
[PATCH v1 net] tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). 4 (4) 2026/06/01 18:10
[syzbot] [net?] WARNING: refcount bug in __inet_csk_reqsk_queue_drop 0 (1) 2026/05/30 05:55

Sample crash report:
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: ktimers/0/16
Modules linked in:
CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: e4 7d d1 0a 67 48 0f b9 3a eb 4a e8 38 3d 23 fd 48 8d 3d e1 7d d1 0a 67 48 0f b9 3a eb 37 e8 25 3d 23 fd 48 8d 3d de 7d d1 0a <67> 48 0f b9 3a eb 24 e8 12 3d 23 fd 48 8d 3d db 7d d1 0a 67 48 0f
RSP: 0000:ffffc90000157948 EFLAGS: 00010246
RAX: ffffffff84a1301b RBX: 0000000000000003 RCX: ffff88801ca98000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffffffff8f72ae00
RBP: ffffffff99ae3b01 R08: ffff88801ca98000 R09: 0000000000000005
R10: 0000000000000100 R11: 0000000000000004 R12: ffff8880425ef568
R13: ffff8880425ef4f8 R14: ffff8880425ef578 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888126386000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7b46710e9c CR3: 000000000dbb6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:400 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 reqsk_put include/net/request_sock.h:136 [inline]
 __inet_csk_reqsk_queue_drop+0x3ce/0x440 net/ipv4/inet_connection_sock.c:1007
 reqsk_timer_handler+0x651/0xdf0 net/ipv4/inet_connection_sock.c:1137
 call_timer_fn+0x192/0x5e0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2374 [inline]
 __run_timer_base+0x6a3/0x9f0 kernel/time/timer.c:2386
 run_timer_base kernel/time/timer.c:2395 [inline]
 run_timer_softirq+0x67/0x170 kernel/time/timer.c:2403
 handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 run_ktimerd+0x69/0x100 kernel/softirq.c:1151
 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	e4 7d                	in     $0x7d,%al
   2:	d1 0a                	rorl   $1,(%rdx)
   4:	67 48 0f b9 3a       	ud1    (%edx),%rdi
   9:	eb 4a                	jmp    0x55
   b:	e8 38 3d 23 fd       	call   0xfd233d48
  10:	48 8d 3d e1 7d d1 0a 	lea    0xad17de1(%rip),%rdi        # 0xad17df8
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 25 3d 23 fd       	call   0xfd233d48
  23:	48 8d 3d de 7d d1 0a 	lea    0xad17dde(%rip),%rdi        # 0xad17e08
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 12 3d 23 fd       	call   0xfd233d48
  36:	48 8d 3d db 7d d1 0a 	lea    0xad17ddb(%rip),%rdi        # 0xad17e18
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/28 06:12 upstream eb3f4b7426cf 4c36e7e5 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2026/05/13 01:20 upstream c21b90f77687 a0949470 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2026/04/28 13:41 upstream 3b3bea6d4b9c b4209743 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2026/02/27 16:57 upstream a75cb869a8cc 2cf092b8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2026/02/18 12:34 upstream c22e26bd0906 39751c21 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2026/01/23 01:29 upstream a66191c590b3 82c9c083 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2025/12/16 06:54 upstream 8f0b4cce4481 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2025/11/14 20:10 upstream d4f8cccc6230 f7988ea4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
2026/05/10 20:37 linux-next e98d21c170b0 29233ece .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING: refcount bug in __inet_csk_reqsk_queue_drop
* Struck through repros no longer work on HEAD.