syzbot


KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send

Status: upstream: reported on 2026/01/25 08:35
Subsystems: can
Labels: race:harmful
[Documentation on labels]
Reported-by: syzbot+75e5e4ae00c3b4bb544e@syzkaller.appspotmail.com
First crash: 7d04h, last: 5d20h
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [can?] KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send 0 (1) 2026/01/25 08:35

Sample crash report:
UDPLite6: UDP-Lite is deprecated and scheduled to be removed in 2025, please contact the netdev mailing list
==================================================================
BUG: KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send

read to 0xffff88811adccc40 of 16 bytes by interrupt on cpu 1:
 bcm_rx_changed net/can/bcm.c:500 [inline]
 bcm_rx_update_and_send+0x37f/0x420 net/can/bcm.c:553
 bcm_rx_handler+0x2b0/0x580 net/can/bcm.c:739
 deliver net/can/af_can.c:575 [inline]
 can_rcv_filter+0x3c6/0x4f0 net/can/af_can.c:636
 can_receive+0xfb/0x1c0 net/can/af_can.c:662
 canfd_rcv+0xed/0x190 net/can/af_can.c:705
 __netif_receive_skb_one_core net/core/dev.c:6152 [inline]
 __netif_receive_skb+0x120/0x270 net/core/dev.c:6265
 process_backlog+0x228/0x420 net/core/dev.c:6617
 __napi_poll+0x5f/0x300 net/core/dev.c:7681
 napi_poll net/core/dev.c:7744 [inline]
 net_rx_action+0x452/0x930 net/core/dev.c:7896
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1063
 smpboot_thread_fn+0x32a/0x510 kernel/smpboot.c:160
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

write to 0xffff88811adccc40 of 16 bytes by task 3847 on cpu 0:
 bcm_rx_setup+0x7c5/0xe00 net/can/bcm.c:1259
 bcm_sendmsg+0x1bb/0x4a0 net/can/bcm.c:1427
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x145/0x170 net/socket.c:742
 ____sys_sendmsg+0x31e/0x4a0 net/socket.c:2592
 ___sys_sendmsg+0x195/0x1e0 net/socket.c:2646
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2683 [inline]
 __se_sys_sendmsg net/socket.c:2681 [inline]
 __x64_sys_sendmsg+0xd4/0x160 net/socket.c:2681
 x64_sys_call+0x17ba/0x3000 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3847 Comm: syz.0.79 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/20 09:20 upstream 24d479d26b25 572effc1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send
2026/01/19 01:36 upstream e84d960149e7 20d37d28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcm_rx_setup / bcm_rx_update_and_send
* Struck through repros no longer work on HEAD.