Fix potential NULL pointer dereference before calling EVP_SignInit

Closes phpGH-13870.

Author: icy17

NEWS

@@ -22,6 +22,7 @@ PHP                                                                        NEWS
     filename causes a NULL pointer dereference). (nielsdos)
   . Fixed bug GH-13833 (Applying zero offset to null pointer in zend_hash.c).
     (nielsdos)
+  . Fix potential NULL pointer dereference before calling EVP_SignInit. (icy17)
 
 - PHPDBG:
   . Fixed bug GH-13827 (Null pointer access of type 'zval' in phpdbg_frame).

ext/phar/util.c

@@ -1884,6 +1884,13 @@ int phar_create_signature(phar_archive_data *phar, php_stream *fp, char **signat
 			}
 
 			md_ctx = EVP_MD_CTX_create();
+			if (md_ctx == NULL) {
+				EVP_PKEY_free(key);
+				if (error) {
+					spprintf(error, 0, "unable to initialize openssl signature for phar \"%s\"", phar->fname);
+				}
+				return FAILURE;
+			}
 
 			siglen = EVP_PKEY_size(key);
 			sigbuf = emalloc(siglen + 1);