syzbot


KCSAN: data-race in copy_mm / vm_mmap_pgoff

Status: moderation: reported on 2025/11/22 14:15
Subsystems: mm
[Documentation on labels]
Reported-by: syzbot+2059e2b89f863d20238b@syzkaller.appspotmail.com
First crash: 5h10m, last: 5h10m

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

read-write to 0xffff8881022ed738 of 4 bytes by task 17393 on cpu 1:
 do_raw_write_seqcount_begin include/linux/seqlock.h:431 [inline]
 mm_lock_seqcount_begin include/linux/mmap_lock.h:88 [inline]
 mmap_write_lock_killable include/linux/mmap_lock.h:332 [inline]
 vm_mmap_pgoff+0x126/0x2e0 mm/util.c:579
 ksys_mmap_pgoff+0xc2/0x310 mm/mmap.c:604
 x64_sys_call+0x14a3/0x3000 arch/x86/include/generated/asm/syscalls_64.h:10
 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 0xffff8881022ed640 of 1408 bytes by task 17396 on cpu 0:
 dup_mm kernel/fork.c:1483 [inline]
 copy_mm+0xe2/0x370 kernel/fork.c:1541
 copy_process+0xd08/0x2000 kernel/fork.c:2181
 kernel_clone+0x16c/0x5c0 kernel/fork.c:2609
 __do_sys_clone3 kernel/fork.c:2911 [inline]
 __se_sys_clone3+0x1c2/0x200 kernel/fork.c:2890
 __x64_sys_clone3+0x31/0x40 kernel/fork.c:2890
 x64_sys_call+0x1fc9/0x3000 arch/x86/include/generated/asm/syscalls_64.h:436
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 17396 Comm: syz.7.4613 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/22 14:14 upstream 2eba5e05d9bc 4fb8ef37 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in copy_mm / vm_mmap_pgoff
* Struck through repros no longer work on HEAD.