lib/ts_bm: fix integer overflow in pattern length calculation

The ts_bm algorithm stores its good_shift[] table and pattern in a single
allocation sized from the pattern length.  If the good_shift[] 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/20260308202028.2889285-1-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>

diff --git a/lib/ts_bm.c b/lib/ts_bm.c
index eed5967238c5c74cddddb1a200793eba8e0835ab..676105e840052099e18d3e284685d94c3931f388 100644 (file)
--- a/lib/ts_bm.c
+++ b/lib/ts_bm.c
@@ -163,8 +163,22 @@ static struct ts_config *bm_init(const void *pattern, unsigned int len,
        struct ts_config *conf;
        struct ts_bm *bm;
        int i;
-       unsigned int prefix_tbl_len = len * sizeof(unsigned int);
-       size_t priv_size = sizeof(*bm) + len + prefix_tbl_len;
+       unsigned int prefix_tbl_len;
+       size_t priv_size;
+
+       /* Zero-length patterns would underflow bm_find()'s initial shift. */
+       if (unlikely(!len))
+               return ERR_PTR(-EINVAL);
+
+       /*
+        * bm->pattern is stored immediately after the good_shift[] table.
+        * Reject lengths that would wrap while sizing either region.
+        */
+       if (unlikely(check_mul_overflow(len, sizeof(*bm->good_shift),
+                                       &prefix_tbl_len) ||
+                    check_add_overflow(sizeof(*bm), (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))