[PATCH v6 4/8] lib: rsa: fix allocated size for rr and rrtmp in rsa_gen_key_prop()

[Heiko Stuebner]

From: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>

When calculating rrtmp/rr rsa_gen_key_prop() tries to make
(((rlen + 31) >> 5) + 1) steps in the rr uint32_t array and
(((rlen + 7) >> 3) + 1) / 4 steps in uint32_t rrtmp[]
with rlen being num_bits * 2

On a 4096bit key this comes down to to 257 uint32_t elements
in rr and 256 elements in rrtmp but with the current allocation
rr and rrtmp only have 129 uint32_t elements.

On 2048bit keys this works by chance as the defined max_rsa_size=4096
allocates a suitable number of elements, but with an actual 4096bit key
this results in other memory parts getting overwritten.

So as suggested by Heinrich Schuchardt just use the actual bis-size
of the key as base for the size calculation, in turn making the code
compatible to any future keysizes.

Suggested-by: Heinrich Schuchardt <xypron.debian at gmx.de>
Signed-off-by: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
---
changes in v6:
- drop max_rsa_size and use the keysize as base
changes in v4:
- new patch

 lib/rsa/rsa-keyprop.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/lib/rsa/rsa-keyprop.c b/lib/rsa/rsa-keyprop.c
index 4b54db44c4..83b942615f 100644
--- a/lib/rsa/rsa-keyprop.c
+++ b/lib/rsa/rsa-keyprop.c
@@ -654,14 +654,10 @@ int rsa_gen_key_prop(const void *key, uint32_t keylen, struct key_prop **prop)
 {
 	struct rsa_key rsa_key;
 	uint32_t *n = NULL, *rr = NULL, *rrtmp = NULL;
-	const int max_rsa_size = 4096;
 	int rlen, i, ret;
 
 	*prop = calloc(sizeof(**prop), 1);
-	n = calloc(sizeof(uint32_t), 1 + (max_rsa_size >> 5));
-	rr = calloc(sizeof(uint32_t), 1 + (max_rsa_size >> 5));
-	rrtmp = calloc(sizeof(uint32_t), 1 + (max_rsa_size >> 5));
-	if (!(*prop) || !n || !rr || !rrtmp) {
+	if (!(*prop)) {
 		ret = -ENOMEM;
 		goto err;
 	}
@@ -682,6 +678,14 @@ int rsa_gen_key_prop(const void *key, uint32_t keylen, struct key_prop **prop)
 	}
 	memcpy((void *)(*prop)->modulus, &rsa_key.n[i], rsa_key.n_sz - i);
 
+	n = calloc(sizeof(uint32_t), 1 + ((*prop)->num_bits >> 5));
+	rr = calloc(sizeof(uint32_t), 1 + (((*prop)->num_bits * 2) >> 5));
+	rrtmp = calloc(sizeof(uint32_t), 1 + (((*prop)->num_bits * 2) >> 5));
+	if (!n || !rr || !rrtmp) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
 	/* exponent */
 	(*prop)->public_exponent = calloc(1, sizeof(uint64_t));
 	if (!(*prop)->public_exponent) {
-- 
2.26.2