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lib/ts_bm: fix integer overflow in pattern length calculation

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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>
This commit is contained in:
Josh Law
2026-03-08 20:20:27 +00:00
committed by Andrew Morton
parent 7aa89307fc
commit 9003ec6f7f
1 changed files with 16 additions and 2 deletions
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18
lib/ts_bm.c
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@@ -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))