[PATCH v2] crypto: sun4i-ss - clamp PRNG seed length to prevent heap overflow

["Tianchu Chen" <tianchu.chen@linux.dev>]

From: Tianchu Chen <flynnnchen@tencent.com>

sun4i_ss_prng_seed() copies the user-supplied seed into ss->seed
using the user-provided length with no bounds check. The crypto core
does not enforce slen <= seedsize before calling into the driver, so a
userspace caller via AF_ALG setsockopt(ALG_SET_KEY) can pass up to
sysctl_optmem_max bytes, overflowing the fixed-size buffer and
corrupting adjacent heap memory.

Clamp the copy length to the buffer size, matching the approach used by
loongson-rng for oversized seeds.

Discovered by Atuin - Automated Vulnerability Discovery Engine.

Fixes: 6298e948215f ("crypto: sunxi-ss - Add Allwinner Security System crypto accelerator")
Cc: stable@vger.kernel.org
Signed-off-by: Tianchu Chen <flynnnchen@tencent.com>
---
v2: Silently clamp oversized seeds with min_t instead of returning
    -EINVAL (Herbert Xu).

 drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c
index 491fcb7b8..7f6a51dd8 100644
--- a/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c
+++ b/drivers/crypto/allwinner/sun4i-ss/sun4i-ss-prng.c
@@ -8,7 +8,7 @@ int sun4i_ss_prng_seed(struct crypto_rng *tfm, const u8 *seed,
 	struct rng_alg *alg = crypto_rng_alg(tfm);
 
 	algt = container_of(alg, struct sun4i_ss_alg_template, alg.rng);
-	memcpy(algt->ss->seed, seed, slen);
+	memcpy(algt->ss->seed, seed, min_t(unsigned int, slen, sizeof(algt->ss->seed)));
 
 	return 0;
 }
-- 
2.51.0