syzbot

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BUG: KCSAN: data-race in _copy_to_iter / strncpy

write to 0xffff88813ebe9488 of 1 bytes by task 10662 on cpu 0:
 strncpy+0x9b/0x150 lib/string.c:96
 ext4_sample_last_mounted fs/ext4/file.c:866 [inline]
 ext4_file_open+0x367/0x3f0 fs/ext4/file.c:885
 do_dentry_open+0x5c3/0xae0 fs/open.c:929
 vfs_open+0x4a/0x50 fs/open.c:1063
 do_open fs/namei.c:3639 [inline]
 path_openat+0x17f2/0x1d10 fs/namei.c:3796
 do_filp_open+0xf6/0x200 fs/namei.c:3823
 do_sys_openat2+0xab/0x110 fs/open.c:1422
 do_sys_open fs/open.c:1437 [inline]
 __do_sys_openat fs/open.c:1453 [inline]
 __se_sys_openat fs/open.c:1448 [inline]
 __x64_sys_openat+0xf3/0x120 fs/open.c:1448
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88813ebe9400 of 1024 bytes by task 4189 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copyout lib/iov_iter.c:167 [inline]
 _copy_to_iter+0x12b/0x950 lib/iov_iter.c:316
 copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:481
 copy_folio_to_iter include/linux/uio.h:185 [inline]
 filemap_read+0x424/0x680 mm/filemap.c:2703
 blkdev_read_iter+0x217/0x2c0 block/fops.c:730
 call_read_iter include/linux/fs.h:1950 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x3da/0x5c0 fs/read_write.c:470
 ksys_read+0xeb/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+0x42/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 4189 Comm: udevd Not tainted 6.6.0-rc3-syzkaller-00038-g0e945134b680 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
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