syzbot

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BUG: KCSAN: data-race in _copy_to_iter / strncpy

write to 0xffff888124c85488 of 1 bytes by task 2653 on cpu 1:
 strncpy+0xb3/0x160 lib/string.c:114
 ext4_sample_last_mounted fs/ext4/file.c:851 [inline]
 ext4_file_open+0x376/0x400 fs/ext4/file.c:870
 do_dentry_open+0x59a/0x910 fs/open.c:882
 vfs_open+0x43/0x50 fs/open.c:1013
 do_open fs/namei.c:3557 [inline]
 path_openat+0x169d/0x1b00 fs/namei.c:3713
 do_filp_open+0x105/0x220 fs/namei.c:3740
 do_sys_openat2+0xb5/0x2a0 fs/open.c:1310
 do_sys_open fs/open.c:1326 [inline]
 __do_sys_open fs/open.c:1334 [inline]
 __se_sys_open fs/open.c:1330 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1330
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff888124c85400 of 1024 bytes by task 2282 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:120 [inline]
 copyout lib/iov_iter.c:169 [inline]
 _copy_to_iter+0x116/0x8e0 lib/iov_iter.c:527
 copy_page_to_iter+0x333/0x3f0 lib/iov_iter.c:725
 copy_folio_to_iter include/linux/uio.h:169 [inline]
 filemap_read+0x11db/0x1510 mm/filemap.c:2726
 blkdev_read_iter+0x2c6/0x370 block/fops.c:598
 call_read_iter include/linux/fs.h:2185 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x3a5/0x560 fs/read_write.c:470
 ksys_read+0xe8/0x1a0 fs/read_write.c:613
 __do_sys_read fs/read_write.c:623 [inline]
 __se_sys_read fs/read_write.c:621 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 2282 Comm: udevd Not tainted 6.1.0-rc4-syzkaller-00020-gf67dd6ce0723-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
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I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
I/O error, dev loop2, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
udevd[2282]: inotify_add_watch(7, /dev/loop1p2, 10) failed: No such file or directory
udevd[2282]: inotify_add_watch(7, /dev/loop1p2, 10) failed: No such file or directory