CVE-2026-31449

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

ext4: validate p_idx bounds in ext4_ext_correct_indexes

ext4_ext_correct_indexes() walks up the extent tree correcting index entries when the first extent in a leaf is modified. Before accessing path[k].p_idx->ei_block, there is no validation that p_idx falls within the valid range of index entries for that level.

If the on-disk extent header contains a corrupted or crafted eh_entries value, p_idx can point past the end of the allocated buffer, causing a slab-out-of-bounds read.

Fix this by validating path[k].p_idx against EXT_LAST_INDEX() at both access sites: before the while loop and inside it. Return -EFSCORRUPTED if the index pointer is out of range, consistent with how other bounds violations are handled in the ext4 extent tree code.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/01bf1e0b997d82c0e353b51ed74ef99698043c33
• https://git.kernel.org/stable/c/10242e640b36b91ad03d25f3dc77854bbdff8358
• https://git.kernel.org/stable/c/2acb5c12ebd860f30e4faf67e6cc8c44ddfe5fe8
• https://git.kernel.org/stable/c/39d6e2b67651614bac0dc6592fa9836321910067
• https://git.kernel.org/stable/c/407c944f217c17d4343148011acafebc604d55e1
• https://git.kernel.org/stable/c/4d08401aa13f1531216f1a7ae281ca4806e90a5c
• https://git.kernel.org/stable/c/93f2e975ed658ce09db4d4c2877ca2c06540df83
• https://git.kernel.org/stable/c/c5839b34704c9c2f47f079451bdbb22de0da1ed1