params: do not ignore zero-length strings

Prior to this commit, if a string (or octet string) parameter
was present but indicated it was zero-length, we would return success
but with a NULL output value.  This can be problematic in cases where
there is a protocol-level distinction between parameter-absent and
parameter-present-but-zero-length, which is uncommon but can happen.

Since OPENSSL_malloc() returns NULL for zero-length allocation requests,
make a dummy allocation for this case, to give a signal that the string
parameter does exist but has zero length.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11920)

diff --git a/crypto/params.c b/crypto/params.c
index 06ae1bc44f37b98276c6a87063b80c41391a4ca0..9bccc517601b988ec5a19ddf079d1afddb890795 100644 (file)
--- a/crypto/params.c
+++ b/crypto/params.c
@@ -788,8 +788,6 @@ static int get_string_internal(const OSSL_PARAM *p, void **val, size_t max_len,
     if (used_len != NULL)
         *used_len = sz;
 
-    if (sz == 0)
-        return 1;
     if (p->data == NULL)
         return 0;
 
@@ -797,12 +795,13 @@ static int get_string_internal(const OSSL_PARAM *p, void **val, size_t max_len,
         return 1;
 
     if (*val == NULL) {
-        char *const q = OPENSSL_malloc(sz);
+        char *const q = OPENSSL_malloc(sz > 0 ? sz : 1);
 
         if (q == NULL)
             return 0;
         *val = q;
-        memcpy(q, p->data, sz);
+        if (sz != 0)
+            memcpy(q, p->data, sz);
         return 1;
     }
     if (max_len < sz)