syzbot

netlink: 4 bytes leftover after parsing attributes in process `syz.4.1266'.
FAT-fs (loop4): error, invalid access to FAT (entry 0x0fff0000)
FAT-fs (loop4): Filesystem has been set read-only
==================================================================
BUG: KCSAN: data-race in __writeback_single_inode / xas_clear_mark

write to 0xffff88811a039a14 of 4 bytes by task 7369 on cpu 0:
 xa_mark_clear lib/xarray.c:77 [inline]
 xas_clear_mark+0x16b/0x180 lib/xarray.c:932
 __folio_start_writeback+0x231/0x390 mm/page-writeback.c:3053
 __block_write_full_folio+0x53a/0x8f0 fs/buffer.c:1928
 block_write_full_folio+0x2c1/0x2e0 fs/buffer.c:-1
 mpage_write_folio fs/mpage.c:641 [inline]
 mpage_writepages+0x6cf/0x1250 fs/mpage.c:670
 fat_writepages+0x24/0x30 fs/fat/inode.c:200
 do_writepages+0x1c6/0x310 mm/page-writeback.c:2598
 filemap_writeback mm/filemap.c:386 [inline]
 filemap_fdatawrite_range mm/filemap.c:411 [inline]
 file_write_and_wait_range+0x156/0x2c0 mm/filemap.c:785
 __generic_file_fsync+0x46/0x160 fs/libfs.c:1540
 fat_file_fsync+0x49/0x100 fs/fat/file.c:191
 vfs_fsync_range+0x10d/0x130 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2617 [inline]
 generic_file_write_iter+0x1b8/0x2f0 mm/filemap.c:4447
 iter_file_splice_write+0x66b/0xa20 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a039a14 of 4 bytes by task 7366 on cpu 1:
 xa_marked include/linux/xarray.h:424 [inline]
 mapping_tagged include/linux/fs.h:507 [inline]
 __writeback_single_inode+0x201/0x7c0 fs/fs-writeback.c:1788
 writeback_single_inode+0x16d/0x3f0 fs/fs-writeback.c:1858
 sync_inode_metadata+0x5b/0x90 fs/fs-writeback.c:2944
 __generic_file_fsync+0x109/0x160 fs/libfs.c:1551
 fat_file_fsync+0x49/0x100 fs/fat/file.c:191
 vfs_fsync_range+0x10d/0x130 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2617 [inline]
 generic_file_write_iter+0x1b8/0x2f0 mm/filemap.c:4447
 iter_file_splice_write+0x66b/0xa20 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
 splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0xda/0x150 fs/splice.c:1230
 do_sendfile+0x380/0x650 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
 x64_sys_call+0x2db1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0e000021 -> 0x04000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 7366 Comm: syz.4.1266 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================
syz.4.1266: attempt to access beyond end of device
loop4: rw=2049, sector=128, nr_sectors = 1 limit=128
Buffer I/O error on dev loop4, logical block 128, lost async page write