From: Josh Law Date: Sun, 8 Mar 2026 20:20:28 +0000 (+0000) Subject: lib/ts_kmp: fix integer overflow in pattern length calculation X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8cdf30813ea8ce881cecc08664144416dbdb3e16;p=thirdparty%2Fkernel%2Fstable.git lib/ts_kmp: fix integer overflow in pattern length calculation 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 Reviewed-by: Andrew Morton Cc: Signed-off-by: Andrew Morton --- diff --git a/lib/ts_kmp.c b/lib/ts_kmp.c index 5520dc28255a..29466c1803c9 100644 --- a/lib/ts_kmp.c +++ b/lib/ts_kmp.c @@ -94,8 +94,22 @@ static struct ts_config *kmp_init(const void *pattern, unsigned int len, 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))