syzbot


KCSAN: data-race in _copy_to_iter / memcpy_and_pad (3)

Status: moderation: reported on 2025/12/16 21:56
Subsystems: block
[Documentation on labels]
Reported-by: syzbot+d021430ddd367627b89e@syzkaller.appspotmail.com
First crash: 145d, last: 11d
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
0f47a6be-4e12-4ff5-81bf-2078c1006ccd assessment-kcsan Benign: ✅ Confident: ✅ KCSAN: data-race in _copy_to_iter / memcpy_and_pad (3) 2026/01/15 23:53 2026/01/15 23:53 2026/01/15 23:56 a9d6a79219801d2130df3b1a792c57f0e5428e9f
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in _copy_to_iter / memcpy_and_pad block 6 2 353d 354d 0/29 auto-obsoleted due to no activity on 2025/07/17 19:38
upstream KCSAN: data-race in _copy_to_iter / memcpy_and_pad (2) block 6 4 203d 245d 0/29 auto-obsoleted due to no activity on 2025/12/14 18:55

Sample crash report:
EXT4-fs: Journaled quota options ignored when QUOTA feature is enabled
EXT4-fs error (device loop3): ext4_free_branches:1023: inode #11: comm syz.3.10292: invalid indirect mapped block 4294967295 (level 1)
loop3: lost file I/O error report for ino 11 type 5 pos 0x0 len 0x0 error -117
==================================================================
BUG: KCSAN: data-race in _copy_to_iter / memcpy_and_pad

read to 0xffff8881227ee400 of 512 bytes by task 3285 on cpu 1:
 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

write to 0xffff8881227ee5f2 of 14 bytes by task 4465 on cpu 0:
 memcpy_and_pad+0x5a/0x80 lib/string_helpers.c:1009
 ext4_update_super+0x790/0xba0 fs/ext4/super.c:6267
 ext4_commit_super+0x40/0x280 fs/ext4/super.c:6296
 ext4_handle_error+0x452/0x550 fs/ext4/super.c:725
 __ext4_error_inode+0x1bb/0x3c0 fs/ext4/super.c:871
 ext4_free_branches+0x3ce/0x410 fs/ext4/indirect.c:1020
 ext4_ind_truncate+0x482/0x840 fs/ext4/indirect.c:1174
 ext4_truncate+0x66c/0xa10 fs/ext4/inode.c:4669
 ext4_process_orphan+0x110/0x1c0 fs/ext4/orphan.c:337
 ext4_orphan_cleanup+0x69c/0x9f0 fs/ext4/orphan.c:472
 __ext4_fill_super fs/ext4/super.c:5701 [inline]
 ext4_fill_super+0x3408/0x37c0 fs/ext4/super.c:5824
 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:5856
 vfs_get_tree+0x57/0x1d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3758 [inline]
 do_new_mount+0x288/0x8d0 fs/namespace.c:3834
 path_mount+0x4d0/0xbc0 fs/namespace.c:4154
 do_mount fs/namespace.c:4167 [inline]
 __do_sys_mount fs/namespace.c:4383 [inline]
 __se_sys_mount+0x28c/0x2e0 fs/namespace.c:4360
 __x64_sys_mount+0x67/0x80 fs/namespace.c:4360
 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/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: 4465 Comm: syz.3.10292 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================
EXT4-fs error (device loop3): ext4_free_branches:1023: inode #11: comm syz.3.10292: invalid indirect mapped block 4294967295 (level 1)
loop3: lost file I/O error report for ino 11 type 5 pos 0x0 len 0x0 error -117
EXT4-fs (loop3): 2 truncates cleaned up
EXT4-fs (loop3): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
x_tables: duplicate underflow at hook 2
EXT4-fs error (device loop3): ext4_find_dest_de:2050: inode #12: block 7: comm syz.3.10292: bad entry in directory: directory entry overrun - offset=0, inode=4278190093, rec_len=196860, size=56 fake=0

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/29 01:25 upstream dca922e019dd 95008c03 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
2026/04/18 20:46 upstream eb5249b12507 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
2026/03/31 09:29 upstream d0c3bcd5b897 aeea1c72 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
2026/02/16 01:51 upstream 26a4cfaff82a 1e62d198 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
2026/01/27 19:57 upstream 1f97d9dcf536 9a514c2f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
2026/01/06 22:43 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
2025/12/16 21:56 upstream 40fbbd64bba6 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in _copy_to_iter / memcpy_and_pad
* Struck through repros no longer work on HEAD.