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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4a95bc121ccd Merge tag 'rproc-v6.15-fixes' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1600e9f4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ea93cce608593e25
dashboard link: https://syzkaller.appspot.com/bug?extid=f490fb4b87e80227d334
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
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/c157aef2e681/disk-4a95bc12.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/285f64f278b5/vmlinux-4a95bc12.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cef6e2a0d5ae/bzImage-4a95bc12.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f490fb...@syzkaller.appspotmail.com

loop2: detected capacity change from 0 to 512
EXT4-fs: Ignoring removed i_version option
EXT4-fs: Ignoring removed nomblk_io_submit option
[EXT4 FS bs=1024, gc=1, bpg=8192, ipg=32, mo=a842e01c, mo2=0002]
System zones: 1-12
EXT4-fs error (device loop2): ext4_validate_block_bitmap:441: comm syz.2.7352: bg 0: block 328: padding at end of block bitmap is not set
==================================================================
BUG: KCSAN: data-race in _copy_to_iter / memcpy_and_pad

read to 0xffff888119d32400 of 1024 bytes by task 3309 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:300 [inline]
iterate_and_advance include/linux/iov_iter.h:328 [inline]
_copy_to_iter+0x12d/0xdd0 lib/iov_iter.c:185
copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:362
copy_folio_to_iter include/linux/uio.h:198 [inline]
filemap_read+0x413/0x990 mm/filemap.c:2753
blkdev_read_iter+0x22d/0x2e0 block/fops.c:809
new_sync_read fs/read_write.c:489 [inline]
vfs_read+0x5cd/0x6f0 fs/read_write.c:570
ksys_read+0xda/0x1a0 fs/read_write.c:713
__do_sys_read fs/read_write.c:722 [inline]
__se_sys_read fs/read_write.c:720 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:720
x64_sys_call+0x2d77/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff888119d325e0 of 26 bytes by task 18749 on cpu 0:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1004
ext4_update_super+0x790/0xb70 fs/ext4/super.c:6169
ext4_commit_super+0x40/0x280 fs/ext4/super.c:6197
ext4_handle_error+0x451/0x550 fs/ext4/super.c:713
__ext4_error+0x19a/0x320 fs/ext4/super.c:824
ext4_validate_block_bitmap+0x557/0x5a0 fs/ext4/balloc.c:-1
ext4_read_block_bitmap_nowait+0x435/0x680 fs/ext4/balloc.c:557
ext4_mb_init_cache+0x240/0xb60 fs/ext4/mballoc.c:1337
ext4_mb_init_group+0x223/0x3b0 fs/ext4/mballoc.c:1543
ext4_mb_load_buddy_gfp+0x6ed/0x750 fs/ext4/mballoc.c:1613
ext4_mb_clear_bb fs/ext4/mballoc.c:6449 [inline]
ext4_free_blocks+0x758/0x1400 fs/ext4/mballoc.c:6651
ext4_clear_blocks+0x2a2/0x2c0 fs/ext4/indirect.c:888
ext4_free_data fs/ext4/indirect.c:962 [inline]
ext4_ind_truncate+0x599/0x830 fs/ext4/indirect.c:1154
ext4_truncate+0x6cc/0xac0 fs/ext4/inode.c:4234
ext4_evict_inode+0x89c/0xd80 fs/ext4/inode.c:266
evict+0x2e3/0x550 fs/inode.c:810
iput_final fs/inode.c:1898 [inline]
iput+0x447/0x5b0 fs/inode.c:1924
ext4_process_orphan+0x1a9/0x1c0 fs/ext4/orphan.c:360
ext4_orphan_cleanup+0x6a8/0xa00 fs/ext4/orphan.c:474
__ext4_fill_super fs/ext4/super.c:5607 [inline]
ext4_fill_super+0x3171/0x34e0 fs/ext4/super.c:5726
get_tree_bdev_flags+0x28e/0x300 fs/super.c:1636
get_tree_bdev+0x1f/0x30 fs/super.c:1659
ext4_get_tree+0x1c/0x30 fs/ext4/super.c:5758
vfs_get_tree+0x57/0x1d0 fs/super.c:1759
do_new_mount+0x207/0x680 fs/namespace.c:3881
path_mount+0x4a4/0xb20 fs/namespace.c:4208
do_mount fs/namespace.c:4221 [inline]
__do_sys_mount fs/namespace.c:4432 [inline]
__se_sys_mount+0x28f/0x2e0 fs/namespace.c:4409
__x64_sys_mount+0x67/0x80 fs/namespace.c:4409
x64_sys_call+0xd36/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 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: 18749 Comm: syz.2.7352 Not tainted 6.15.0-rc7-syzkaller-00007-g4a95bc121ccd #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================
EXT4-fs error (device loop2) in ext4_mb_clear_bb:6548: Corrupt filesystem
EXT4-fs error (device loop2): ext4_free_branches:1023: inode #13: comm syz.2.7352: invalid indirect mapped block 65280 (level 0)
EXT4-fs error (device loop2): ext4_clear_blocks:876: inode #13: comm syz.2.7352: attempt to clear invalid blocks 33619980 len 1
EXT4-fs error (device loop2): ext4_free_branches:1023: inode #13: comm syz.2.7352: invalid indirect mapped block 1819239214 (level 0)
EXT4-fs error (device loop2): ext4_free_branches:1023: inode #13: comm syz.2.7352: invalid indirect mapped block 1819239214 (level 1)
EXT4-fs (loop2): 1 orphan inode deleted
EXT4-fs (loop2): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.