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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 <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 8cdf3081 9003ec6f

+16 -2
+16 -2
lib/ts_kmp.c
··· 94 94 struct ts_config *conf; 95 95 struct ts_kmp *kmp; 96 96 int i; 97 - unsigned int prefix_tbl_len = len * sizeof(unsigned int); 98 - size_t priv_size = sizeof(*kmp) + len + prefix_tbl_len; 97 + unsigned int prefix_tbl_len; 98 + size_t priv_size; 99 + 100 + /* Zero-length patterns would make kmp_find() read beyond kmp->pattern. */ 101 + if (unlikely(!len)) 102 + return ERR_PTR(-EINVAL); 103 + 104 + /* 105 + * kmp->pattern is stored immediately after the prefix_tbl[] table. 106 + * Reject lengths that would wrap while sizing either region. 107 + */ 108 + if (unlikely(check_mul_overflow(len, sizeof(*kmp->prefix_tbl), 109 + &prefix_tbl_len) || 110 + check_add_overflow(sizeof(*kmp), (size_t)len, &priv_size) || 111 + check_add_overflow(priv_size, prefix_tbl_len, &priv_size))) 112 + return ERR_PTR(-EINVAL); 99 113 100 114 conf = alloc_ts_config(priv_size, gfp_mask); 101 115 if (IS_ERR(conf))