[moderation] [ext4?] KCSAN: data-race in _copy_to_iter / string

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6613476e225e Linux 6.8-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16521915e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=5197e0a6c8448ad3
dashboard link: https://syzkaller.appspot.com/bug?extid=85ef9006893186caee83
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/61d720b37887/disk-6613476e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d122725c1ed5/vmlinux-6613476e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/85b4e6b79b60/bzImage-6613476e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+85ef90...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / string

write to 0xffff888128cc1050 of 1 bytes by task 10150 on cpu 0:
string_nocheck lib/vsprintf.c:650 [inline]
string+0x16c/0x200 lib/vsprintf.c:728
bdev_name+0x140/0x240 lib/vsprintf.c:968
pointer+0x5e3/0xd10 lib/vsprintf.c:2474
vsnprintf+0x861/0xe20 lib/vsprintf.c:2828
snprintf+0x87/0xb0 lib/vsprintf.c:2959
ext4_multi_mount_protect+0x4cc/0x5e0 fs/ext4/mmp.c:386
__ext4_fill_super fs/ext4/super.c:5363 [inline]
ext4_fill_super+0x290c/0x39a0 fs/ext4/super.c:5703
get_tree_bdev+0x250/0x2d0 fs/super.c:1619
ext4_get_tree+0x1c/0x20 fs/ext4/super.c:5735
vfs_get_tree+0x51/0x1b0 fs/super.c:1784
do_new_mount+0x227/0x690 fs/namespace.c:3352
path_mount+0x496/0xb30 fs/namespace.c:3679
do_mount fs/namespace.c:3692 [inline]
__do_sys_mount fs/namespace.c:3898 [inline]
__se_sys_mount+0x27f/0x2d0 fs/namespace.c:3875
__x64_sys_mount+0x67/0x80 fs/namespace.c:3875
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888128cc1000 of 512 bytes by task 22947 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:29 [inline]
iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
iterate_and_advance include/linux/iov_iter.h:271 [inline]
_copy_to_iter+0x126/0xb20 lib/iov_iter.c:186
copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:381
copy_folio_to_iter include/linux/uio.h:181 [inline]
filemap_read+0x42c/0x680 mm/filemap.c:2654
blkdev_read_iter+0x217/0x2c0 block/fops.c:757
call_read_iter include/linux/fs.h:2079 [inline]
new_sync_read fs/read_write.c:395 [inline]
vfs_read+0x5ab/0x6a0 fs/read_write.c:476
ksys_read+0xeb/0x1a0 fs/read_write.c:619
__do_sys_read fs/read_write.c:629 [inline]
__se_sys_read fs/read_write.c:627 [inline]
__x64_sys_read+0x42/0x50 fs/read_write.c:627
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x59/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22947 Comm: udevd Not tainted 6.8.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
==================================================================


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[syzbot]

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