CVE-2026-80673: ntfs: bound the look-ahead attribute-list entry in ntfs_external_attr_find()

CVE-2026-80673: ntfs: bound the look-ahead attribute-list entry in ntfs_external_attr_find()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

ntfs: bound the look-ahead attribute-list entry in ntfs_external_attr_find()

When resolving an attribute lookup with a non-zero @lowest_vcn,
ntfs_external_attr_find() peeks at the next $ATTRIBUTE_LIST entry to
decide whether to keep searching, but bounds that not-yet-validated
entry only with "(u8 *)next_al_entry + 6 < al_end" (which proves just
bytes 0..6 are in range) and "(u8 *)next_al_entry + length <= al_end"
with an attacker-controlled, non-8-aligned length. It then reads
next_al_entry->lowest_vcn (an __le64 at offset 8) and the name at
next_al_entry->name_offset, both of which can lie past al_end -- the
exact end of the kvmalloc'd attribute-list buffer (allocated at the
on-disk attr_list_size, no rounding). A crafted on-disk $ATTRIBUTE_LIST
whose last entry sits a few bytes before al_end therefore yields a slab
out-of-bounds read when the inode is read.

Validate the look-ahead entry with ntfs_attr_list_entry_is_valid() (added
in patch 1/3) before dereferencing lowest_vcn and the name, so the same
fixed-header, length and name bounds the main attribute-list walk uses now
guard this read too.

The Linux kernel CVE team has assigned CVE-2026-80673 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 7.1 with commit 1e9ea7e04472d4e5e12e58c881eaacfb3e49b669 and fixed in 7.1.5 with commit 44885c9b45eb4082fb7f558590d84bb254a08e94
	Issue introduced in 7.1 with commit 1e9ea7e04472d4e5e12e58c881eaacfb3e49b669 and fixed in 7.2 with commit 344b18f389f9934d59c7b0cf3d20541ea2e0da58

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80673
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ntfs/attrib.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/44885c9b45eb4082fb7f558590d84bb254a08e94
	https://git.kernel.org/stable/c/344b18f389f9934d59c7b0cf3d20541ea2e0da58