[moderation] [bpf?] KCSAN: data-race in __bpf_get_stackid / bcmp

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 52da431bf03b Merge tag 'libnvdimm-fixes-6.16-rc3' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=169aa370580000
kernel config: https://syzkaller.appspot.com/x/.config?x=25d7df3a6a1d1ea6
dashboard link: https://syzkaller.appspot.com/bug?extid=505324320caac3303e6f
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [and...@kernel.org a...@kernel.org b...@vger.kernel.org dan...@iogearbox.net edd...@gmail.com hao...@google.com john.fa...@gmail.com jo...@kernel.org kps...@kernel.org linux-...@vger.kernel.org marti...@linux.dev s...@fomichev.me so...@kernel.org yongho...@linux.dev]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6cf1b0066c08/disk-52da431b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a3e72711158a/vmlinux-52da431b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a403ba239c60/bzImage-52da431b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+505324...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __bpf_get_stackid / bcmp

write to 0xffff88811c5a8228 of 160 bytes by task 3646 on cpu 1:
__bpf_get_stackid+0x761/0x800 kernel/bpf/stackmap.c:288
____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
bpf_get_stackid+0xee/0x120 kernel/bpf/stackmap.c:300
____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1811 [inline]
bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1800
bpf_prog_e6fc920cfeff8120+0x2a/0x32
bpf_dispatcher_nop_func include/linux/bpf.h:1322 [inline]
__bpf_prog_run include/linux/filter.h:718 [inline]
bpf_prog_run include/linux/filter.h:725 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2258 [inline]
bpf_trace_run3+0x10f/0x1d0 kernel/trace/bpf_trace.c:2300
__do_trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
kmem_cache_free+0x257/0x300 mm/slub.c:4744
skb_kfree_head net/core/skbuff.c:1046 [inline]
skb_free_head+0x87/0x150 net/core/skbuff.c:1060
skb_release_data+0x33b/0x370 net/core/skbuff.c:1087
skb_release_all net/core/skbuff.c:1152 [inline]
__kfree_skb+0x44/0x150 net/core/skbuff.c:1166
sk_skb_reason_drop+0xbd/0x270 net/core/skbuff.c:1204
kfree_skb_reason include/linux/skbuff.h:1275 [inline]
__skb_queue_purge_reason include/linux/skbuff.h:3355 [inline]
__skb_queue_purge include/linux/skbuff.h:3360 [inline]
tipc_mcast_xmit+0x806/0xcb0 net/tipc/bcast.c:428
tipc_send_group_bcast+0x5d9/0x6c0 net/tipc/socket.c:1130
__tipc_sendmsg+0x186/0x1b00 net/tipc/socket.c:-1
tipc_sendmsg+0x3e/0x60 net/tipc/socket.c:1399
sock_sendmsg_nosec net/socket.c:712 [inline]
__sock_sendmsg+0x142/0x180 net/socket.c:727
____sys_sendmsg+0x345/0x4e0 net/socket.c:2566
___sys_sendmsg+0x17b/0x1d0 net/socket.c:2620
__sys_sendmmsg+0x178/0x300 net/socket.c:2709
__do_sys_sendmmsg net/socket.c:2736 [inline]
__se_sys_sendmmsg net/socket.c:2733 [inline]
__x64_sys_sendmmsg+0x57/0x70 net/socket.c:2733
x64_sys_call+0x2f2f/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:308
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811c5a8258 of 8 bytes by task 3656 on cpu 0:
memcmp lib/string.c:683 [inline]
bcmp+0x23/0x90 lib/string.c:715
memcmp include/linux/fortify-string.h:727 [inline]
__bpf_get_stackid+0x371/0x800 kernel/bpf/stackmap.c:279
____bpf_get_stackid kernel/bpf/stackmap.c:324 [inline]
bpf_get_stackid+0xee/0x120 kernel/bpf/stackmap.c:300
____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1811 [inline]
bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1800
bpf_prog_e6fc920cfeff8120+0x2a/0x32
bpf_dispatcher_nop_func include/linux/bpf.h:1322 [inline]
__bpf_prog_run include/linux/filter.h:718 [inline]
bpf_prog_run include/linux/filter.h:725 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2258 [inline]
bpf_trace_run3+0x10f/0x1d0 kernel/trace/bpf_trace.c:2300
__do_trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
trace_kmem_cache_free include/trace/events/kmem.h:114 [inline]
kmem_cache_free+0x257/0x300 mm/slub.c:4744
__d_free fs/dcache.c:345 [inline]
dentry_free fs/dcache.c:440 [inline]
__dentry_kill+0x3d1/0x4b0 fs/dcache.c:688
dput+0x5e/0xd0 fs/dcache.c:911
__fput+0x444/0x650 fs/file_table.c:473
____fput+0x1c/0x30 fs/file_table.c:493
task_work_run+0x12e/0x1a0 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xe4/0x100 kernel/entry/common.c:114
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffffffff8191e014 -> 0xffffffff8445d7b4

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3656 Comm: syz.1.76 Not tainted 6.16.0-rc2-syzkaller-00047-g52da431bf03b #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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