CVE-2026-98591: bpf: Fix bounds check for skb-backed dynptrs

CVE-2026-98591: bpf: Fix bounds check for skb-backed dynptrs

[Greg Kroah-Hartman]

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

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

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

bpf: Fix bounds check for skb-backed dynptrs

The skb_pointer_if_linear() function checks whether a
memory region of length len starting at offset off into
the skb is in the linear area, and returns a pointer to
the region if so. The check currently subtracts between
skb_headlen and offset of the check, and since skb_headlen
is unsigned the subtraction can underflow. This causes the
bounds check to spuriously pass and generate an arbitrary
pointer of the form *(skb->data + off).

The only user of this helper is currently skb-backed BPF
dynptr code. Returning the wrong pointer leads to the
dynptr erroneously being backed with invalid memory.

Ensure the subtraction cannot underflow, and fail the check if
it would. Use u64 arithmetic to also prevent overflow when
calculating (skb_headlen(skb) - off) since off is unsigned.

The Linux kernel CVE team has assigned CVE-2026-98591 to this issue.


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

	Issue introduced in 6.6 with commit 6f5a630d7c57cd79b1f526a95e757311e32d41e5 and fixed in 6.6.158 with commit 1b923538598be768e9f2f258a77a083d00e0c78b
	Issue introduced in 6.6 with commit 6f5a630d7c57cd79b1f526a95e757311e32d41e5 and fixed in 6.12.112 with commit 37877a24758068742fef687a7cf5362360dde1d1
	Issue introduced in 6.6 with commit 6f5a630d7c57cd79b1f526a95e757311e32d41e5 and fixed in 6.18.55 with commit 1196903a27cac5c929c7517e987a8d159f20c5e5
	Issue introduced in 6.6 with commit 6f5a630d7c57cd79b1f526a95e757311e32d41e5 and fixed in 7.2.9 with commit 39ffceaddb10753eac12785dba6ac0673860b4ac
	Issue introduced in 6.6 with commit 6f5a630d7c57cd79b1f526a95e757311e32d41e5 and fixed in 7.3-rc5 with commit ed6eec97b534979dcf28b40c389cee57bd6561d4

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-2026-98591
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:
	include/linux/skbuff.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/1b923538598be768e9f2f258a77a083d00e0c78b
	https://git.kernel.org/stable/c/37877a24758068742fef687a7cf5362360dde1d1
	https://git.kernel.org/stable/c/1196903a27cac5c929c7517e987a8d159f20c5e5
	https://git.kernel.org/stable/c/39ffceaddb10753eac12785dba6ac0673860b4ac
	https://git.kernel.org/stable/c/ed6eec97b534979dcf28b40c389cee57bd6561d4