CVE-2024-39276

/// Technical description

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

ext4: fix mb_cache_entry's e_refcnt leak in ext4_xattr_block_cache_find()

Syzbot reports a warning as follows:

============================================

WARNING: CPU: 0 PID: 5075 at fs/mbcache.c:419 mb_cache_destroy+0x224/0x290

Modules linked in:

CPU: 0 PID: 5075 Comm: syz-executor199 Not tainted 6.9.0-rc6-gb947cc5bf6d7

RIP: 0010:mb_cache_destroy+0x224/0x290 fs/mbcache.c:419

Call Trace:

<TASK>

ext4_put_super+0x6d4/0xcd0 fs/ext4/super.c:1375

generic_shutdown_super+0x136/0x2d0 fs/super.c:641

kill_block_super+0x44/0x90 fs/super.c:1675

ext4_kill_sb+0x68/0xa0 fs/ext4/super.c:7327

[...]

============================================

This is because when finding an entry in ext4_xattr_block_cache_find(), if

ext4_sb_bread() returns -ENOMEM, the ce's e_refcnt, which has already grown

in the __entry_find(), won't be put away, and eventually trigger the above

issue in mb_cache_destroy() due to reference count leakage.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References