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KCSAN: data-race in bcmp / parse_build_id

Status: auto-obsoleted due to no activity on 2026/02/28 21:04
Subsystems: bpf
[Documentation on labels]
Reported-by: syzbot+34ed7a3bbe17728f901f@syzkaller.appspotmail.com
First crash: 184d, last: 87d
▶ ▼ ✨ AI Jobs (7)
ID Workflow Result Correct Bug Created Started Finished Revision Error
bffb9bce-b39e-4013-8bb9-2196c1667691 assessment-kcsan Benign: ✅  Confident: ✅  ❓ KCSAN: data-race in bcmp / parse_build_id 2026/03/31 12:12 2026/03/31 12:26 2026/03/31 13:12 d0af506ef4609d1bffbbbbae776b857a63d84b20
228fa79f-b547-4b40-aa18-42b289115f09 repro 💥 KCSAN: data-race in bcmp / parse_build_id 2026/03/26 15:57 2026/03/26 15:57 2026/03/26 16:05 50cdcaa1adff11dc8afdfa7ec9e390b9c5b72c3f failed to deserialize syzkaller program: wrong int arg *prog.UnionType line #1:155: r0 = bpf$MAP_CREATE(0x0, &(0x7f0000000000)=@base={0x7, 0x4, 0x140, 0x1, 0x20, 0xffffffffffffffff, 0x0, "", 0x0, 0xffffffffffffffff, 0x0, 0x0, 0x0, 0x0, 0x0<<<!!ERROR!!>>>, 0x0}, AUTO)
f8250c1f-879f-4d56-8bc6-ee719619701c repro 💥 KCSAN: data-race in bcmp / parse_build_id 2026/03/26 12:49 2026/03/26 12:49 2026/03/26 15:57 fca8d36012560bb3df56f0d849e5588ffe9eb992 Aborted: assigned agent restarted
dab8acf6-2ebb-425d-be8a-c861441fccf0 repro 💥 KCSAN: data-race in bcmp / parse_build_id 2026/03/26 10:43 2026/03/26 10:44 2026/03/26 12:49 c6143aacd8e1a01f2482ab5eec709f9949710cee Aborted: assigned agent restarted
50dd7d43-ddc6-4c5b-9f2d-9316e8ac31ae repro 💥 KCSAN: data-race in bcmp / parse_build_id 2026/03/23 14:12 2026/03/24 08:22 2026/03/24 09:31 971831e4896625f799f350fe4439dc0774b7154a+ timedout after 1h0m0s ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "36" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/91b604bc6761bd44e9752ec29e9d9a77d12acb8c" "-s" "bzImage" "compile_commands.json"] * * Restart config... * * * Memory initialization * Initialize kernel stack variables at function entry 1. no automatic stack variable initialization (weakest) (INIT_STACK_NONE) 2. pattern-init everything (strongest) (INIT_STACK_ALL_PATTERN) > 3. zero-init everything (strongest and safest) (INIT_STACK_ALL_ZERO) choice[1-3?]: 3 Poison kernel stack before returning from syscalls (KSTACK_ERASE) [N/y/?] (NEW) Error in reading or end of file. Enable heap memory zeroing on allocation by default (INIT_ON_ALLOC_DEFAULT_ON) [Y/n/?] y Enable heap memory zeroing on free by default (INIT_ON_FREE_DEFAULT_ON) [N/y/?] n Enable register zeroing on function exit (ZERO_CALL_USED_REGS) [N/y/?] n
d91b896e-fffc-4021-99f6-4cd915913efc assessment-kcsan Benign: ❌  Confident: ✅  ❓ KCSAN: data-race in bcmp / parse_build_id 2026/02/25 02:53 2026/02/25 02:53 2026/02/25 03:09 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
711fe6b1-d1e3-4624-a866-91be264146a3 assessment-kcsan 💥 KCSAN: data-race in bcmp / parse_build_id 2026/01/15 14:45 2026/01/15 14:45 2026/01/15 14:48 a9d6a79219801d2130df3b1a792c57f0e5428e9f LLM did not call tool to set outputs

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

write to 0xffffc9000f831cf4 of 20 bytes by task 18187 on cpu 0:
 parse_build_id+0x249/0x2b0 lib/buildid.c:184
 get_build_id_64 lib/buildid.c:263 [inline]
 __build_id_parse+0x253/0x4a0 lib/buildid.c:308
 build_id_parse_nofault+0x27/0x40 lib/buildid.c:327
 fetch_build_id kernel/bpf/stackmap.c:152 [inline]
 stack_map_get_build_id_offset+0x226/0x530 kernel/bpf/stackmap.c:197
 __bpf_get_stackid+0x60b/0x7d0 kernel/bpf/stackmap.c:289
 ____bpf_get_stackid kernel/bpf/stackmap.c:344 [inline]
 bpf_get_stackid+0xf3/0x130 kernel/bpf/stackmap.c:323
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1628 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1617
 bpf_prog_ff69ba342f4eb966+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run4+0x117/0x1e0 kernel/trace/bpf_trace.c:2118
 __do_trace_mm_page_alloc include/trace/events/kmem.h:180 [inline]
 trace_mm_page_alloc include/trace/events/kmem.h:180 [inline]
 __alloc_frozen_pages_noprof+0x336/0x360 mm/page_alloc.c:5232
 alloc_pages_mpol+0xb3/0x260 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x39/0x80 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1890 [inline]
 shmem_alloc_and_add_folio mm/shmem.c:1932 [inline]
 shmem_get_folio_gfp+0x3cf/0xd50 mm/shmem.c:2556
 shmem_get_folio mm/shmem.c:2662 [inline]
 shmem_write_begin+0xfc/0x1f0 mm/shmem.c:3315
 generic_perform_write+0x184/0x490 mm/filemap.c:4314
 shmem_file_write_iter+0xc5/0xf0 mm/shmem.c:3490
 __kernel_write_iter+0x2d6/0x540 fs/read_write.c:619
 dump_emit_page fs/coredump.c:1298 [inline]
 dump_user_range+0x61e/0x8f0 fs/coredump.c:1372
 elf_core_dump+0x1de7/0x1f80 fs/binfmt_elf.c:2111
 coredump_write+0xacf/0xdf0 fs/coredump.c:1049
 do_coredump fs/coredump.c:1126 [inline]
 vfs_coredump+0x24f7/0x2e60 fs/coredump.c:1200
 get_signal+0xd84/0xf70 kernel/signal.c:3019
 arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:75 [inline]
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:270 [inline]
 irqentry_exit_to_user_mode include/linux/irq-entry-common.h:339 [inline]
 irqentry_exit+0xfb/0x560 kernel/entry/common.c:196
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

read to 0xffffc9000f831d00 of 8 bytes by task 18266 on cpu 1:
 memcmp lib/string.c:683 [inline]
 bcmp+0x23/0x90 lib/string.c:715
 memcmp include/linux/fortify-string.h:727 [inline]
 __bpf_get_stackid+0x648/0x7d0 kernel/bpf/stackmap.c:292
 ____bpf_get_stackid kernel/bpf/stackmap.c:344 [inline]
 bpf_get_stackid+0xf3/0x130 kernel/bpf/stackmap.c:323
 ____bpf_get_stackid_raw_tp kernel/trace/bpf_trace.c:1628 [inline]
 bpf_get_stackid_raw_tp+0xf6/0x120 kernel/trace/bpf_trace.c:1617
 bpf_prog_ff69ba342f4eb966+0x2a/0x32
 bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2075 [inline]
 bpf_trace_run4+0x117/0x1e0 kernel/trace/bpf_trace.c:2118
 __do_trace_mm_page_alloc include/trace/events/kmem.h:180 [inline]
 trace_mm_page_alloc include/trace/events/kmem.h:180 [inline]
 __alloc_frozen_pages_noprof+0x336/0x360 mm/page_alloc.c:5232
 alloc_pages_mpol+0xb3/0x260 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x39/0x80 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1890 [inline]
 shmem_alloc_and_add_folio mm/shmem.c:1932 [inline]
 shmem_get_folio_gfp+0x3cf/0xd50 mm/shmem.c:2556
 shmem_fault+0xf6/0x250 mm/shmem.c:2757
 __do_fault+0xbc/0x200 mm/memory.c:5320
 do_read_fault mm/memory.c:5755 [inline]
 do_fault mm/memory.c:5889 [inline]
 do_pte_missing mm/memory.c:4401 [inline]
 handle_pte_fault mm/memory.c:6273 [inline]
 __handle_mm_fault mm/memory.c:6411 [inline]
 handle_mm_fault+0xfab/0x2c60 mm/memory.c:6580
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0x1024/0x1ed0 mm/gup.c:1428
 populate_vma_page_range mm/gup.c:1860 [inline]
 __mm_populate+0x243/0x3a0 mm/gup.c:1963
 mm_populate include/linux/mm.h:3701 [inline]
 vm_mmap_pgoff+0x232/0x2e0 mm/util.c:586
 ksys_mmap_pgoff+0xc2/0x310 mm/mmap.c:604
 x64_sys_call+0x16bb/0x3000 arch/x86/include/generated/asm/syscalls_64.h:10
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xf042c5f12da5e5e6

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 18266 Comm: syz.9.4420 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/03 21:03 upstream 805f9a061372 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcmp / parse_build_id
2025/11/14 18:02 upstream 6da43bbeb691 f7988ea4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcmp / parse_build_id
2025/11/14 18:02 upstream 6da43bbeb691 f7988ea4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcmp / parse_build_id
2025/10/30 08:39 upstream e53642b87a4f fd2207e7 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcmp / parse_build_id
2025/09/28 15:25 upstream 51a24b7deaae 001c9061 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in bcmp / parse_build_id
* Struck through repros no longer work on HEAD.