[moderation] [exfat?] KCSAN: data-race in _copy_to_iter / fat32_ent_put (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8b69c0475871 Merge tag 'input-for-v7.2-rc0-2' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17cd8261580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=50264f69ab1e622312e7
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
CC: [hiro...@mail.parknet.co.jp linki...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org sj155...@samsung.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/13586095b06f/disk-8b69c047.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/affe0f8cbabd/vmlinux-8b69c047.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bd2466f5b2e9/bzImage-8b69c047.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+50264f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / fat32_ent_put

read-write to 0xffff88811c3ee074 of 4 bytes by task 18099 on cpu 1:
fat32_ent_put+0x4e/0x90 fs/fat/fatent.c:194
fat_alloc_clusters+0x55e/0xc40 fs/fat/fatent.c:508
fat_alloc_new_dir+0xbb/0x550 fs/fat/dir.c:1159
vfat_mkdir+0xa4/0x210 fs/fat/namei_vfat.c:862
vfs_mkdir+0x28a/0x3e0 fs/namei.c:5272
filename_mkdirat+0x138/0x300 fs/namei.c:5305
__do_sys_mkdir fs/namei.c:5332 [inline]
__se_sys_mkdir+0x31/0xf0 fs/namei.c:5329
__x64_sys_mkdir+0x31/0x40 fs/namei.c:5329
x64_sys_call+0x2eab/0x3020 arch/x86/include/generated/asm/syscalls_64.h:84
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811c3ee000 of 512 bytes by task 3620 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+0x174/0x210 lib/iov_iter.c:374
copy_folio_to_iter include/linux/uio.h:204 [inline]
filemap_read+0x3ed/0xa20 mm/filemap.c:2865
blkdev_read_iter+0x21e/0x2d0 block/fops.c:830
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x699/0x7c0 fs/read_write.c:574
ksys_read+0xdc/0x1a0 fs/read_write.c:716
__do_sys_read fs/read_write.c:725 [inline]
__se_sys_read fs/read_write.c:723 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:723
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+0x136/0x3c0 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: 3620 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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