In the Linux kernel, the following vulnerability has been resolved:

ext4: fix OOB read when checking dotdot dir

Mounting a corrupted filesystem with directory which contains '.' dir
entry with rec_len == block size results in out-of-bounds read (later
on, when the corrupted directory is removed).

ext4_empty_dir() assumes every ext4 directory contains at least '.'
and '..' as directory entries in the first data block. It first loads
the '.' dir entry, performs sanity checks by calling ext4_check_dir_entry()
and then uses its rec_len member to compute the location of '..' dir
entry (in ext4_next_entry). It assumes the '..' dir entry fits into the
same data block.

If the rec_len of '.' is precisely one block (4KB), it slips through the
sanity checks (it is considered the last directory entry in the data
block) and leaves "struct ext4_dir_entry_2 *de" point exactly past the
memory slot allocated to the data block. The following call to
ext4_check_dir_entry() on new value of de then dereferences this pointer
which results in out-of-bounds mem access.

Fix this by extending __ext4_check_dir_entry() to check for '.' dir
entries that reach the end of data block. Make sure to ignore the phony
dir entries for checksum (by checking name_len for non-zero).

Note: This is reported by KASAN as use-after-free in case another
structure was recently freed from the slot past the bound, but it is
really an OOB read.

This issue was found by syzkaller tool.

Call Trace:
[   38.594108] BUG: KASAN: slab-use-after-free in __ext4_check_dir_entry+0x67e/0x710
[   38.594649] Read of size 2 at addr ffff88802b41a004 by task syz-executor/5375
[   38.595158]
[   38.595288] CPU: 0 UID: 0 PID: 5375 Comm: syz-executor Not tainted 6.14.0-rc7 #1
[   38.595298] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   38.595304] Call Trace:
[   38.595308]  <TASK>
[   38.595311]  dump_stack_lvl+0xa7/0xd0
[   38.595325]  print_address_description.constprop.0+0x2c/0x3f0
[   38.595339]  ? __ext4_check_dir_entry+0x67e/0x710
[   38.595349]  print_report+0xaa/0x250
[   38.595359]  ? __ext4_check_dir_entry+0x67e/0x710
[   38.595368]  ? kasan_addr_to_slab+0x9/0x90
[   38.595378]  kasan_report+0xab/0xe0
[   38.595389]  ? __ext4_check_dir_entry+0x67e/0x710
[   38.595400]  __ext4_check_dir_entry+0x67e/0x710
[   38.595410]  ext4_empty_dir+0x465/0x990
[   38.595421]  ? __pfx_ext4_empty_dir+0x10/0x10
[   38.595432]  ext4_rmdir.part.0+0x29a/0xd10
[   38.595441]  ? __dquot_initialize+0x2a7/0xbf0
[   38.595455]  ? __pfx_ext4_rmdir.part.0+0x10/0x10
[   38.595464]  ? __pfx___dquot_initialize+0x10/0x10
[   38.595478]  ? down_write+0xdb/0x140
[   38.595487]  ? __pfx_down_write+0x10/0x10
[   38.595497]  ext4_rmdir+0xee/0x140
[   38.595506]  vfs_rmdir+0x209/0x670
[   38.595517]  ? lookup_one_qstr_excl+0x3b/0x190
[   38.595529]  do_rmdir+0x363/0x3c0
[   38.595537]  ? __pfx_do_rmdir+0x10/0x10
[   38.595544]  ? strncpy_from_user+0x1ff/0x2e0
[   38.595561]  __x64_sys_unlinkat+0xf0/0x130
[   38.595570]  do_syscall_64+0x5b/0x180
[   38.595583]  entry_SYSCALL_64_after_hwframe+0x76/0x7e

https://git.kernel.org/stable/c/52a5509ab19a5d3afe301165d9b5787bba34d842

https://git.kernel.org/stable/c/53bc45da8d8da92ec07877f5922b130562eb4b00

https://git.kernel.org/stable/c/89503e5eae64637d0fa2218912b54660effe7d93

https://git.kernel.org/stable/c/ac28c5684c1cdab650a7e5065b19e91577d37a4b

https://git.kernel.org/stable/c/b47584c556444cf7acb66b26a62cbc348eb92b78

https://git.kernel.org/stable/c/b7531a4f99c3887439d778afaf418d1a01a5f01b

https://git.kernel.org/stable/c/d5e206778e96e8667d3bde695ad372c296dc9353

https://git.kernel.org/stable/c/e47f472a664d70a3d104a6c2a035cdff55a719b4