CVE-2026-89761: apparmor: fix out-of-bounds write when null terminating a label vec

CVE-2026-89761: apparmor: fix out-of-bounds write when null terminating a label vec

[Greg Kroah-Hartman]

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

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

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

apparmor: fix out-of-bounds write when null terminating a label vec

aa_vec_unique() null terminates at vec[n - dups] when VEC_FLAG_TERMINATE
is passed. If the components are all distinct no duplicates are dropped,
dups is 0 and the terminator goes to vec[n], so the caller has to provide
room for n + 1 entries.

aa_label_strn_parse() sets up its vector with vec_setup(profile, vec, len,
gfp) and then calls aa_vec_unique(vec, len, VEC_FLAG_TERMINATE), but
vec_setup() does not reserve the terminator entry. Up to LOCAL_VEC_ENTRIES
it uses the local array of LOCAL_VEC_ENTRIES pointers, above that it
allocates exactly len pointers. The terminator therefore lands one entry
past the end of the local array when len is LOCAL_VEC_ENTRIES, and one
entry past the end of the allocation when len is larger.

len comes from the number of "//&" separated components in the label name
and label_count_strn_entries() does not bound it. An unprivileged task
reaches the parse by writing to /proc/self/attr/apparmor/current or through
lsm_set_self_attr(2), both of which go through do_setattr(), and the name
is parsed before the change_profile permission is checked.
The query_label() path behind the securityfs .access file, which is
mode 0666, performs no permission check at all. Every component has to
resolve to a loaded profile, so a system with policy loaded is required.

The other two VEC_FLAG_TERMINATE users work on a label vec that
aa_label_alloc() has already sized with "+ 1 for null terminator entry on
vec". Reserve the same entry in vec_setup() and DEFINE_VEC(). Passing
len + 1 from the caller instead would move len == LOCAL_VEC_ENTRIES out of
the local array and into kzalloc().

The Linux kernel CVE team has assigned CVE-2026-89761 to this issue.


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

	Issue introduced in 4.13 with commit f1bd904175e8190ce14aedee37e207ab51fe3b30 and fixed in 6.12.109 with commit 9124e078ea2250d8d01d2162a550acb01ef5bf48
	Issue introduced in 4.13 with commit f1bd904175e8190ce14aedee37e207ab51fe3b30 and fixed in 6.18.50 with commit 28069434aef66b9d084f0609b7a29c171846815e
	Issue introduced in 4.13 with commit f1bd904175e8190ce14aedee37e207ab51fe3b30 and fixed in 7.2.4 with commit 36bdd0b45ec3f4822832a56e9db8674c8450dfce
	Issue introduced in 4.13 with commit f1bd904175e8190ce14aedee37e207ab51fe3b30 and fixed in 7.3-rc1 with commit 9f1e40193eef7f047e6b77cfb4b4cafdecd7a123

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-2026-89761
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:
	security/apparmor/include/label.h


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/9124e078ea2250d8d01d2162a550acb01ef5bf48
	https://git.kernel.org/stable/c/28069434aef66b9d084f0609b7a29c171846815e
	https://git.kernel.org/stable/c/36bdd0b45ec3f4822832a56e9db8674c8450dfce
	https://git.kernel.org/stable/c/9f1e40193eef7f047e6b77cfb4b4cafdecd7a123