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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>

authored by

Josh Law and committed by
Andrew Morton 9003ec6f 7aa89307

+16 -2
+16 -2
lib/ts_bm.c
··· 163 163 struct ts_config *conf; 164 164 struct ts_bm *bm; 165 165 int i; 166 - unsigned int prefix_tbl_len = len * sizeof(unsigned int); 167 - size_t priv_size = sizeof(*bm) + len + prefix_tbl_len; 166 + unsigned int prefix_tbl_len; 167 + size_t priv_size; 168 + 169 + /* Zero-length patterns would underflow bm_find()'s initial shift. */ 170 + if (unlikely(!len)) 171 + return ERR_PTR(-EINVAL); 172 + 173 + /* 174 + * bm->pattern is stored immediately after the good_shift[] table. 175 + * Reject lengths that would wrap while sizing either region. 176 + */ 177 + if (unlikely(check_mul_overflow(len, sizeof(*bm->good_shift), 178 + &prefix_tbl_len) || 179 + check_add_overflow(sizeof(*bm), (size_t)len, &priv_size) || 180 + check_add_overflow(priv_size, prefix_tbl_len, &priv_size))) 181 + return ERR_PTR(-EINVAL); 168 182 169 183 conf = alloc_ts_config(priv_size, gfp_mask); 170 184 if (IS_ERR(conf))