syzbot


KCSAN: data-race in _copy_to_iter / fat32_ent_put (6)

Status: moderation: reported on 2026/04/21 09:06
Subsystems: exfat
[Documentation on labels]
Reported-by: syzbot+23cbb05142ae920887fd@syzkaller.appspotmail.com
First crash: 1d04h, last: 1d04h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
6f84e432-f684-4724-97f5-39d2c11c71e1 assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in _copy_to_iter / fat32_ent_put (6) 2026/04/21 09:06 2026/04/21 09:06 2026/04/21 09:26 3f2e655b2741ba770abc65f58ac94b7e897edae8
Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in _copy_to_iter / fat32_ent_put (5) exfat 6 2 91d 125d 0/29 auto-obsoleted due to no activity on 2026/03/18 08:45
upstream KCSAN: data-race in _copy_to_iter / fat32_ent_put (2) exfat 6 1 1176d 1176d 0/29 auto-obsoleted due to no activity on 2023/04/12 08:12
upstream KCSAN: data-race in _copy_to_iter / fat32_ent_put (4) exfat 6 1 657d 657d 0/29 auto-obsoleted due to no activity on 2024/08/07 19:41
upstream KCSAN: data-race in _copy_to_iter / fat32_ent_put exfat 6 1 1247d 1247d 0/29 auto-obsoleted due to no activity on 2023/01/02 12:34
upstream KCSAN: data-race in _copy_to_iter / fat32_ent_put (3) exfat 6 1 1096d 1096d 0/29 auto-obsoleted due to no activity on 2023/05/26 23:35

Sample crash report:
==================================================================
BUG: KCSAN: data-race in _copy_to_iter / fat32_ent_put

read-write to 0xffff88813fb44028 of 4 bytes by task 12527 on cpu 1:
 fat32_ent_put+0x4e/0x90 fs/fat/fatent.c:194
 fat_alloc_clusters+0x57b/0xc50 fs/fat/fatent.c:508
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x25e/0x5f0 fs/fat/inode.c:190
 __block_write_begin_int+0x400/0xf90 fs/buffer.c:2035
 block_write_begin fs/buffer.c:2146 [inline]
 cont_write_begin+0x5fe/0x970 fs/buffer.c:2484
 fat_write_begin+0x52/0xe0 fs/fat/inode.c:230
 cont_expand_zero fs/buffer.c:2412 [inline]
 cont_write_begin+0x1b0/0x970 fs/buffer.c:2474
 fat_write_begin+0x52/0xe0 fs/fat/inode.c:230
 generic_perform_write+0x183/0x490 mm/filemap.c:4325
 __generic_file_write_iter+0xec/0x120 mm/filemap.c:4439
 generic_file_write_iter+0x8d/0x310 mm/filemap.c:4468
 do_iter_readv_writev+0x4fd/0x5a0 fs/read_write.c:-1
 vfs_writev+0x2e1/0x900 fs/read_write.c:1059
 do_pwritev fs/read_write.c:1155 [inline]
 __do_sys_pwritev2 fs/read_write.c:1213 [inline]
 __se_sys_pwritev2+0xfc/0x1c0 fs/read_write.c:1204
 __x64_sys_pwritev2+0x67/0x80 fs/read_write.c:1204
 x64_sys_call+0xe07/0x3020 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88813fb44000 of 512 bytes by task 3889 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+0x178/0x210 lib/iov_iter.c:374
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 filemap_read+0x407/0xa10 mm/filemap.c:2857
 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/0x3b0 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: 3889 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/21 09:06 upstream b4e07588e743 3f2e655b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / fat32_ent_put
* Struck through repros no longer work on HEAD.