CVE-2024-42305

/// Technical description

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

ext4: check dot and dotdot of dx_root before making dir indexed

Syzbot reports a issue as follows:

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

BUG: unable to handle page fault for address: ffffed11022e24fe

PGD 23ffee067 P4D 23ffee067 PUD 0

Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI

CPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e689933 #0

Call Trace:

<TASK>

make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341

ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451

ext4_rename fs/ext4/namei.c:3936 [inline]

ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214

[...]

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

The immediate cause of this problem is that there is only one valid dentry

for the block to be split during do_split, so split==0 results in out of

bounds accesses to the map triggering the issue.

do_split

unsigned split

dx_make_map

count = 1

split = count/2 = 0;

/// 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