Fix handling of NULL sig parameter in ECDSA_sign and similar

The problem is, that it almost works to pass sig=NULL to the
ECDSA_sign, ECDSA_sign_ex and DSA_sign, to compute the necessary
space for the resulting signature.
But since the ECDSA signature is non-deterministic
(except when ECDSA_sign_setup/ECDSA_sign_ex are used)
the resulting length may be different when the API is called again.
This can easily cause random memory corruption.
Several internal APIs had the same issue, but since they are
never called with sig=NULL, it is better to make them return an
error in that case, instead of making the code more complex.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23529)

(cherry picked from commit 1fa2bf9b1885d2e87524421fea5041d40149cffa)

5 files changed, 49 insertions, 6 deletions

diff --git a/crypto/dsa/dsa_sign.c b/crypto/dsa/dsa_sign.c
index ddfbfa18af..2f963af8e1 100644
--- a/crypto/dsa/dsa_sign.c
+++ b/crypto/dsa/dsa_sign.c
@@ -156,6 +156,11 @@ int ossl_dsa_sign_int(int type, const unsigned char *dgst, int dlen,
 {
     DSA_SIG *s;
 
+    if (sig == NULL) {
+        *siglen = DSA_size(dsa);
+        return 1;
+    }
+
     /* legacy case uses the method table */
     if (dsa->libctx == NULL || dsa->meth != DSA_get_default_method())
         s = DSA_do_sign(dgst, dlen, dsa);
@@ -165,7 +170,7 @@ int ossl_dsa_sign_int(int type, const unsigned char *dgst, int dlen,
         *siglen = 0;
         return 0;
     }
-    *siglen = i2d_DSA_SIG(s, sig != NULL ? &sig : NULL);
+    *siglen = i2d_DSA_SIG(s, &sig);
     DSA_SIG_free(s);
     return 1;
 }
diff --git a/crypto/ec/ecdsa_ossl.c b/crypto/ec/ecdsa_ossl.c
index 0bf4635e2f..0bdf45e6e7 100644
--- a/crypto/ec/ecdsa_ossl.c
+++ b/crypto/ec/ecdsa_ossl.c
@@ -70,6 +70,11 @@ int ossl_ecdsa_sign(int type, const unsigned char *dgst, int dlen,
 {
     ECDSA_SIG *s;
 
+    if (sig == NULL && (kinv == NULL || r == NULL)) {
+        *siglen = ECDSA_size(eckey);
+        return 1;
+    }
+
     s = ECDSA_do_sign_ex(dgst, dlen, kinv, r, eckey);
     if (s == NULL) {
         *siglen = 0;
diff --git a/crypto/sm2/sm2_sign.c b/crypto/sm2/sm2_sign.c
index ff5be9b73e..09e542990b 100644
--- a/crypto/sm2/sm2_sign.c
+++ b/crypto/sm2/sm2_sign.c
@@ -442,6 +442,11 @@ int ossl_sm2_internal_sign(const unsigned char *dgst, int dgstlen,
     int sigleni;
     int ret = -1;
 
+    if (sig == NULL) {
+        ERR_raise(ERR_LIB_SM2, ERR_R_PASSED_NULL_PARAMETER);
+        goto done;
+    }
+
     e = BN_bin2bn(dgst, dgstlen, NULL);
     if (e == NULL) {
        ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
@@ -454,7 +459,7 @@ int ossl_sm2_internal_sign(const unsigned char *dgst, int dgstlen,
         goto done;
     }
 
-    sigleni = i2d_ECDSA_SIG(s, sig != NULL ? &sig : NULL);
+    sigleni = i2d_ECDSA_SIG(s, &sig);
     if (sigleni < 0) {
        ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
        goto done;
diff --git a/test/dsatest.c b/test/dsatest.c
index 5fa83020f8..73c6827bb0 100644
--- a/test/dsatest.c
+++ b/test/dsatest.c
@@ -332,6 +332,7 @@ static int test_dsa_sig_infinite_loop(void)
     BIGNUM *p = NULL, *q = NULL, *g = NULL, *priv = NULL, *pub = NULL, *priv2 = NULL;
     BIGNUM *badq = NULL, *badpriv = NULL;
     const unsigned char msg[] = { 0x00 };
+    unsigned int signature_len0;
     unsigned int signature_len;
     unsigned char signature[64];
 
@@ -375,10 +376,13 @@ static int test_dsa_sig_infinite_loop(void)
         goto err;
 
     /* Test passing signature as NULL */
-    if (!TEST_true(DSA_sign(0, msg, sizeof(msg), NULL, &signature_len, dsa)))
+    if (!TEST_true(DSA_sign(0, msg, sizeof(msg), NULL, &signature_len0, dsa))
+        || !TEST_int_gt(signature_len0, 0))
         goto err;
 
-    if (!TEST_true(DSA_sign(0, msg, sizeof(msg), signature, &signature_len, dsa)))
+    if (!TEST_true(DSA_sign(0, msg, sizeof(msg), signature, &signature_len, dsa))
+        || !TEST_int_gt(signature_len, 0)
+        || !TEST_int_le(signature_len, signature_len0))
         goto err;
 
     /* Test using a private key of zero fails - this causes an infinite loop without the retry test */
diff --git a/test/ecdsatest.c b/test/ecdsatest.c
index 33a52eb1b5..ded41be5bd 100644
--- a/test/ecdsatest.c
+++ b/test/ecdsatest.c
@@ -350,15 +350,39 @@ static int test_builtin_as_sm2(int n)
 static int test_ecdsa_sig_NULL(void)
 {
     int ret;
+    unsigned int siglen0;
     unsigned int siglen;
     unsigned char dgst[128] = { 0 };
     EC_KEY *eckey = NULL;
+    unsigned char *sig = NULL;
+    BIGNUM *kinv = NULL, *rp = NULL;
 
     ret = TEST_ptr(eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1))
           && TEST_int_eq(EC_KEY_generate_key(eckey), 1)
-          && TEST_int_eq(ECDSA_sign(0, dgst, sizeof(dgst), NULL, &siglen, eckey), 1)
-          && TEST_int_gt(siglen, 0);
+          && TEST_int_eq(ECDSA_sign(0, dgst, sizeof(dgst), NULL, &siglen0,
+                                    eckey), 1)
+          && TEST_int_gt(siglen0, 0)
+          && TEST_ptr(sig = OPENSSL_malloc(siglen0))
+          && TEST_int_eq(ECDSA_sign(0, dgst, sizeof(dgst), sig, &siglen,
+                                    eckey), 1)
+          && TEST_int_gt(siglen, 0)
+          && TEST_int_le(siglen, siglen0)
+          && TEST_int_eq(ECDSA_verify(0, dgst, sizeof(dgst), sig, siglen,
+                                      eckey), 1)
+          && TEST_int_eq(ECDSA_sign_setup(eckey, NULL, &kinv, &rp), 1)
+          && TEST_int_eq(ECDSA_sign_ex(0, dgst, sizeof(dgst), NULL, &siglen,
+                                       kinv, rp, eckey), 1)
+          && TEST_int_gt(siglen, 0)
+          && TEST_int_le(siglen, siglen0)
+          && TEST_int_eq(ECDSA_sign_ex(0, dgst, sizeof(dgst), sig, &siglen0,
+                                       kinv, rp, eckey), 1)
+          && TEST_int_eq(siglen, siglen0)
+          && TEST_int_eq(ECDSA_verify(0, dgst, sizeof(dgst), sig, siglen,
+                                      eckey), 1);
     EC_KEY_free(eckey);
+    OPENSSL_free(sig);
+    BN_free(kinv);
+    BN_free(rp);
     return ret;
 }