Make DSA_sign() test for negative p,q,g values.

Related to #20268

DSA_sign() assumes that the signature passed in is related to DSA_size().
If q is negative then DSA_size() actually fails and returns 0.

A test that tries to allocate the signature buffer using DSA_size() and then
pass it to DSA_sign() will then either.

(1) Have a signature buffer of NULL. In this case it was leaking data
returned via i2d_DSA_SIG.

(2) Cause a seg fault because we created a buffer that was not large
enough to hold the signature. As it already checked zero we also now
check for negative values also.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/20553)

1 files changed, 1 insertions, 1 deletions

diff --git a/crypto/dsa/dsa_sign.c b/crypto/dsa/dsa_sign.c
index 96d103d6f2..487a7e2516 100644
--- a/crypto/dsa/dsa_sign.c
+++ b/crypto/dsa/dsa_sign.c
@@ -167,7 +167,7 @@ int ossl_dsa_sign_int(int type, const unsigned char *dgst, int dlen,
         *siglen = 0;
         return 0;
     }
-    *siglen = i2d_DSA_SIG(s, &sig);
+    *siglen = i2d_DSA_SIG(s, sig != NULL ? &sig : NULL);
     DSA_SIG_free(s);
     return 1;
 }