[moderation] [block?] KCSAN: data-race in _copy_to_iter / memcpy_and_pad (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6ab41fca2e80 Merge tag 'timers-urgent-2025-09-07' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=177d7134580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6e0c213d0735f5dd
dashboard link: https://syzkaller.appspot.com/bug?extid=7a4ccac88a3cc49e3b8b
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ax...@kernel.dk linux...@vger.kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/741152900af0/disk-6ab41fca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e4a5fd55ddee/vmlinux-6ab41fca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/52ae33dc3ef8/bzImage-6ab41fca.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7a4cca...@syzkaller.appspotmail.com

loop8: detected capacity change from 0 to 1024
EXT4-fs (loop8): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
==================================================================
BUG: KCSAN: data-race in _copy_to_iter / memcpy_and_pad

read to 0xffff88813a8f0400 of 1024 bytes by task 5110 on cpu 1:
instrument_copy_to_user include/linux/instrumented.h:113 [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+0x130/0xe70 lib/iov_iter.c:185
copy_page_to_iter+0x18f/0x2d0 lib/iov_iter.c:362
copy_folio_to_iter include/linux/uio.h:204 [inline]
filemap_read+0x407/0xa00 mm/filemap.c:2763
blkdev_read_iter+0x22d/0x2e0 block/fops.c:849
new_sync_read fs/read_write.c:491 [inline]
vfs_read+0x64c/0x770 fs/read_write.c:572
ksys_read+0xda/0x1a0 fs/read_write.c:715
__do_sys_read fs/read_write.c:724 [inline]
__se_sys_read fs/read_write.c:722 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:722
x64_sys_call+0x27bc/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:1
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

write to 0xffff88813a8f0488 of 10 bytes by task 16712 on cpu 0:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1007
ext4_sample_last_mounted fs/ext4/file.c:879 [inline]
ext4_file_open+0x53d/0x600 fs/ext4/file.c:901
do_dentry_open+0x649/0xa20 fs/open.c:965
vfs_open+0x37/0x1e0 fs/open.c:1095
do_open fs/namei.c:3887 [inline]
path_openat+0x1c5e/0x2170 fs/namei.c:4046
do_filp_open+0x109/0x230 fs/namei.c:4073
do_sys_openat2+0xa6/0x110 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_openat fs/open.c:1466 [inline]
__se_sys_openat fs/open.c:1461 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1461
x64_sys_call+0x2e9c/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:258
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: 16712 Comm: syz.8.4028 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================


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