Fix memory leaks in CTLOG_new_from_base64

Move the call to ct_base64_decode(), which allocates, until after
the check for NULL output parameter.

Also place a cap on the number of padding characters used to decrement
the output length -- any more than two '='s is not permitted in a
well-formed base64 text.  Prior to this change, ct_base64_decode() would
return a length of -1 along with allocated storage for an input of
"====".

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3379)

1 files changed, 8 insertions, 4 deletions

diff --git a/crypto/ct/ct_b64.c b/crypto/ct/ct_b64.c
index f0bf3aff29..109ffcdcf2 100644
--- a/crypto/ct/ct_b64.c
+++ b/crypto/ct/ct_b64.c
@@ -24,7 +24,7 @@
 static int ct_base64_decode(const char *in, unsigned char **out)
 {
     size_t inlen = strlen(in);
-    int outlen;
+    int outlen, i;
     unsigned char *outbuf = NULL;
 
     if (inlen == 0) {
@@ -45,9 +45,12 @@ static int ct_base64_decode(const char *in, unsigned char **out)
         goto err;
     }
 
-    /* Subtract padding bytes from |outlen| */
+    /* Subtract padding bytes from |outlen|.  Any more than 2 is malformed. */
+    i = 0;
     while (in[--inlen] == '=') {
         --outlen;
+        if (++i > 2)
+            goto err;
     }
 
     *out = outbuf;
@@ -132,7 +135,7 @@ SCT *SCT_new_from_base64(unsigned char version, const char *logid_base64,
 int CTLOG_new_from_base64(CTLOG **ct_log, const char *pkey_base64, const char *name)
 {
     unsigned char *pkey_der = NULL;
-    int pkey_der_len = ct_base64_decode(pkey_base64, &pkey_der);
+    int pkey_der_len;
     const unsigned char *p;
     EVP_PKEY *pkey = NULL;
 
@@ -141,7 +144,8 @@ int CTLOG_new_from_base64(CTLOG **ct_log, const char *pkey_base64, const char *n
         return 0;
     }
 
-    if (pkey_der_len <= 0) {
+    pkey_der_len = ct_base64_decode(pkey_base64, &pkey_der);
+    if (pkey_der_len < 0) {
         CTerr(CT_F_CTLOG_NEW_FROM_BASE64, CT_R_LOG_CONF_INVALID_KEY);
         return 0;
     }