CVE-2022-49879

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

ext4: fix BUG_ON() when directory entry has invalid rec_len

The rec_len field in the directory entry has to be a multiple of 4. A corrupted filesystem image can be used to hit a BUG() in ext4_rec_len_to_disk(), called from make_indexed_dir().

————[ cut here ]———— kernel BUG at fs/ext4/ext4.h:2413! … RIP: 0010:make_indexed_dir+0x53f/0x5f0 … Call Trace: ? add_dirent_to_buf+0x1b2/0x200 ext4_add_entry+0x36e/0x480 ext4_add_nondir+0x2b/0xc0 ext4_create+0x163/0x200 path_openat+0x635/0xe90 do_filp_open+0xb4/0x160 ? __create_object.isra.0+0x1de/0x3b0 ? _raw_spin_unlock+0x12/0x30 do_sys_openat2+0x91/0x150 __x64_sys_open+0x6c/0xa0 do_syscall_64+0x3c/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0

The fix simply adds a call to ext4_check_dir_entry() to validate the directory entry, returning -EFSCORRUPTED if the entry is invalid.

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/156451a67b93986fb07c274ef6995ff40766c5ad
• https://git.kernel.org/stable/c/17a0bc9bd697f75cfdf9b378d5eb2d7409c91340
• https://git.kernel.org/stable/c/2fa24d0274fbf913b56ee31f15bc01168669d909
• https://git.kernel.org/stable/c/999cff2b6ce3b45c08abf793bf55534777421327
• https://git.kernel.org/stable/c/ce1ee2c8827fb6493e91acbd50f664cf2a972c3d