pkcs7: provide fuzz harness

This allows for pkcs7 fuzz testing with OSS-Fuzz.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>

programs/fuzz/.gitignore

@@ -1,6 +1,7 @@
 fuzz_client
 fuzz_dtlsclient
 fuzz_dtlsserver
+fuzz_pkcs7
 fuzz_privkey
 fuzz_pubkey
 fuzz_server

programs/fuzz/CMakeLists.txt

@@ -12,6 +12,7 @@ set(executables_no_common_c
     fuzz_x509crl
     fuzz_x509crt
     fuzz_x509csr
+    fuzz_pkcs7
 )
 
 set(executables_with_common_c

programs/fuzz/fuzz_pkcs7.c

@@ -0,0 +1,19 @@
+#include <stdint.h>
+#include "mbedtls/pkcs7.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+#ifdef MBEDTLS_PKCS7_C
+    mbedtls_pkcs7 pkcs7;
+
+    mbedtls_pkcs7_init( &pkcs7 );
+
+    mbedtls_pkcs7_parse_der( &pkcs7, Data, Size );
+
+    mbedtls_pkcs7_free( &pkcs7 );
+#else
+    (void) Data;
+    (void) Size;
+#endif
+
+    return 0;
+}

programs/fuzz/fuzz_pkcs7.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 65535