KCSAN: data-race in igmp_rcv / igmp_rcv (2)

Status: fixed on 2026/05/22 04:12
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+ae9a171f239b14485310@syzkaller.appspotmail.com
Fix commit: c6bebaa744f7 ipv4: igmp: annotate data-races in igmp_heard_query()
First crash: 141d, last: 141d
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
c6b01896 assessment-kcsan Benign: ✅ Confident: ✅ ❓ KCSAN: data-race in igmp_rcv / igmp_rcv (2) 2026/03/31 12:13 2026/03/31 14:08 2026/03/31 14:55 aeea1c72
fc3b3456 assessment-kcsan Benign: ✅ Confident: ✅ ❓ KCSAN: data-race in igmp_rcv / igmp_rcv (2) 2026/03/17 05:40 2026/03/17 05:40 2026/03/17 05:43 f84caa2f
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH net] ipv4: igmp: annotate data-races in igmp_heard_query() 2 (2) 2026/05/02 00:20
[syzbot] [net?] KCSAN: data-race in igmp_rcv / igmp_rcv (2) 0 (1) 2026/04/30 16:42
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in igmp_rcv / igmp_rcv net 6 1 456d 456d 0/29 auto-obsoleted due to no activity on 2025/07/01 09:48

Sample crash report:
==================================================================
BUG: KCSAN: data-race in igmp_rcv / igmp_rcv

read to 0xffff88810a66f058 of 8 bytes by task 5213 on cpu 1:
 igmp_heard_query net/ipv4/igmp.c:1025 [inline]
 igmp_rcv+0x10af/0x1200 net/ipv4/igmp.c:1103
 ip_protocol_deliver_rcu+0x421/0x790 net/ipv4/ip_input.c:207
 ip_local_deliver_finish+0x1fc/0x2f0 net/ipv4/ip_input.c:241
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ip_local_deliver+0xe8/0x1e0 net/ipv4/ip_input.c:262
 dst_input include/net/dst.h:480 [inline]
 ip_rcv_finish+0x188/0x1a0 net/ipv4/ip_input.c:453
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ip_rcv+0x62/0x160 net/ipv4/ip_input.c:573
 __netif_receive_skb_one_core net/core/dev.c:6164 [inline]
 __netif_receive_skb net/core/dev.c:6277 [inline]
 netif_receive_skb_internal net/core/dev.c:6363 [inline]
 netif_receive_skb+0x137/0x530 net/core/dev.c:6422
 tun_rx_batched+0x106/0x440 drivers/net/tun.c:1485
 tun_get_user+0x2011/0x27c0 drivers/net/tun.c:1953
 tun_chr_write_iter+0x15e/0x210 drivers/net/tun.c:1999
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff88810a66f058 of 8 bytes by task 5212 on cpu 0:
 igmp_heard_query net/ipv4/igmp.c:1026 [inline]
 igmp_rcv+0x10eb/0x1200 net/ipv4/igmp.c:1103
 ip_protocol_deliver_rcu+0x421/0x790 net/ipv4/ip_input.c:207
 ip_local_deliver_finish+0x1fc/0x2f0 net/ipv4/ip_input.c:241
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ip_local_deliver+0xe8/0x1e0 net/ipv4/ip_input.c:262
 dst_input include/net/dst.h:480 [inline]
 ip_rcv_finish+0x188/0x1a0 net/ipv4/ip_input.c:453
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ip_rcv+0x62/0x160 net/ipv4/ip_input.c:573
 __netif_receive_skb_one_core net/core/dev.c:6164 [inline]
 __netif_receive_skb net/core/dev.c:6277 [inline]
 netif_receive_skb_internal net/core/dev.c:6363 [inline]
 netif_receive_skb+0x137/0x530 net/core/dev.c:6422
 tun_rx_batched+0x106/0x440 drivers/net/tun.c:1485
 tun_get_user+0x2011/0x27c0 drivers/net/tun.c:1953
 tun_chr_write_iter+0x15e/0x210 drivers/net/tun.c:1999
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000003e8 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5212 Comm: syz.1.463 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/17 05:40 upstream 2d1373e4246d 0737c18f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in igmp_rcv / igmp_rcv
* Struck through repros no longer work on HEAD.