[PATCH v2 1/2] lib/ts_bm: fix integer overflow in pattern length calculation

[Josh Law <hlcj1234567@gmail.com>]

From: Josh Law <objecting@objecting.org>

The ts_bm algorithm computes the required allocation size by
multiplying the pattern length by the size of an integer. If the
pattern length is sufficiently large, this can overflow the 32-bit
unsigned int before it is widened to size_t. This could result in an
undersized allocation and a subsequent heap buffer overflow when
copying the pattern.

Fix this by explicitly checking that the length does not exceed
the maximum safe threshold before calculating the buffer sizes.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/ts_bm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/ts_bm.c b/lib/ts_bm.c
index eed5967238c5..01ea0a93cf6e 100644
--- a/lib/ts_bm.c
+++ b/lib/ts_bm.c
@@ -166,6 +166,9 @@ static struct ts_config *bm_init(const void *pattern, unsigned int len,
 	unsigned int prefix_tbl_len = len * sizeof(unsigned int);
 	size_t priv_size = sizeof(*bm) + len + prefix_tbl_len;
 
+	if (unlikely(len == 0 || len > (UINT_MAX - sizeof(*bm)) / (sizeof(unsigned int) + 1)))
+		return ERR_PTR(-EINVAL);
+
 	conf = alloc_ts_config(priv_size, gfp_mask);
 	if (IS_ERR(conf))
 		return conf;
-- 
2.43.0