syzbot


KCSAN: data-race in _copy_to_iter / string (5)

Status: moderation: reported on 2026/02/08 03:18
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+5b7175d55be83d4f0d1b@syzkaller.appspotmail.com
First crash: 23d, last: 5d14h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
1b35cb82-712a-42ed-9ad5-1b4213c23aa3 assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in _copy_to_iter / string (5) 2026/02/25 01:23 2026/02/25 01:23 2026/02/25 01:26 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9
7ddae2da-c866-42c6-8d15-c47414565319 assessment-kcsan 💥 KCSAN: data-race in _copy_to_iter / string (5) 2026/02/08 03:18 2026/02/08 03:18 2026/02/08 03:18 97745f52f5b9361548048f53f0b3b51b9313fedf fork/exec ./syz-agent: no such file or directory
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in _copy_to_iter / string (2) ext4 6 2 691d 710d 0/29 auto-obsoleted due to no activity on 2024/05/15 22:06
upstream KCSAN: data-race in _copy_to_iter / string (4) ext4 6 1 426d 426d 0/29 auto-obsoleted due to no activity on 2025/02/26 06:42
upstream KCSAN: data-race in _copy_to_iter / string (3) ext4 6 2 550d 558d 0/29 auto-obsoleted due to no activity on 2024/10/03 11:49
upstream KCSAN: data-race in _copy_to_iter / string ext4 6 1 770d 770d 0/29 auto-obsoleted due to no activity on 2024/02/26 12:58

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

write to 0xffff888189feb050 of 1 bytes by task 14362 on cpu 1:
 string_nocheck lib/vsprintf.c:659 [inline]
 string+0x187/0x220 lib/vsprintf.c:737
 bdev_name+0xd7/0x2b0 lib/vsprintf.c:977
 pointer+0x549/0xcb0 lib/vsprintf.c:2588
 vsnprintf+0x491/0x860 lib/vsprintf.c:2952
 snprintf+0x86/0xb0 lib/vsprintf.c:3042
 ext4_multi_mount_protect+0x4e4/0x600 fs/ext4/mmp.c:382
 __ext4_fill_super fs/ext4/super.c:5464 [inline]
 ext4_fill_super+0x22e6/0x37c0 fs/ext4/super.c:5791
 get_tree_bdev_flags+0x291/0x300 fs/super.c:1694
 get_tree_bdev+0x1f/0x30 fs/super.c:1717
 ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5823
 vfs_get_tree+0x57/0x1d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3760 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3836
 path_mount+0x4d0/0xbc0 fs/namespace.c:4146
 do_mount fs/namespace.c:4159 [inline]
 __do_sys_mount fs/namespace.c:4348 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4325
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4325
 x64_sys_call+0x2d61/0x3020 arch/x86/include/generated/asm/syscalls_64.h:166
 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

read to 0xffff888189feb000 of 512 bytes by task 9063 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:130 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x130/0xea0 lib/iov_iter.c:197
 copy_page_to_iter+0x18f/0x2d0 lib/iov_iter.c:374
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 filemap_read+0x407/0xa10 mm/filemap.c:2851
 blkdev_read_iter+0x22d/0x2e0 block/fops.c:855
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x6c0/0x7f0 fs/read_write.c:574
 ksys_read+0xdc/0x1a0 fs/read_write.c:717
 __do_sys_read fs/read_write.c:726 [inline]
 __se_sys_read fs/read_write.c:724 [inline]
 __x64_sys_read+0x40/0x50 fs/read_write.c:724
 x64_sys_call+0x2886/0x3020 arch/x86/include/generated/asm/syscalls_64.h:1
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 9063 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/25 19:09 upstream 7dff99b35460 94a9671e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / string
2026/02/08 03:18 upstream e7aa57247700 4c131dc4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / string
* Struck through repros no longer work on HEAD.