queue-6.18/lib-ts_kmp-fix-integer-overflow-in-pattern-length-calculation.patch

From 8cdf30813ea8ce881cecc08664144416dbdb3e16 Mon Sep 17 00:00:00 2001
From: Josh Law <objecting@objecting.org>
Date: Sun, 8 Mar 2026 20:20:28 +0000
Subject: lib/ts_kmp: fix integer overflow in pattern length calculation

From: Josh Law <objecting@objecting.org>

commit 8cdf30813ea8ce881cecc08664144416dbdb3e16 upstream.

The ts_kmp algorithm stores its prefix_tbl[] table and pattern in a single
allocation sized from the pattern length.  If the prefix_tbl[] size
calculation wraps, the resulting allocation can be too small and
subsequent pattern copies can overflow it.

Fix this by rejecting zero-length patterns and by using overflow helpers
before calculating the combined allocation size.


This fixes a potential heap overflow.  The pattern length calculation can
wrap during a size_t addition, leading to an undersized allocation.
Because the textsearch library is reachable from userspace via Netfilter's
xt_string module, this is a security risk that should be backported to LTS
kernels.

Link: https://lkml.kernel.org/r/20260308202028.2889285-2-objecting@objecting.org
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 lib/ts_kmp.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

--- a/lib/ts_kmp.c
+++ b/lib/ts_kmp.c
@@ -94,8 +94,22 @@ static struct ts_config *kmp_init(const
 	struct ts_config *conf;
 	struct ts_kmp *kmp;
 	int i;
-	unsigned int prefix_tbl_len = len * sizeof(unsigned int);
-	size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len;
+	unsigned int prefix_tbl_len;
+	size_t priv_size;
+
+	/* Zero-length patterns would make kmp_find() read beyond kmp->pattern. */
+	if (unlikely(!len))
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * kmp->pattern is stored immediately after the prefix_tbl[] table.
+	 * Reject lengths that would wrap while sizing either region.
+	 */
+	if (unlikely(check_mul_overflow(len, sizeof(*kmp->prefix_tbl),
+					&prefix_tbl_len) ||
+		     check_add_overflow(sizeof(*kmp), (size_t)len, &priv_size) ||
+		     check_add_overflow(priv_size, prefix_tbl_len, &priv_size)))
+		return ERR_PTR(-EINVAL);
 
 	conf = alloc_ts_config(priv_size, gfp_mask);
 	if (IS_ERR(conf))