Fix instances of pointer addition with the NULL pointer

Addition using the NULL pointer (even when adding 0) is undefined
behaviour. Recent versions of ubsan are now complaining about this, so
we fix various instances.
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13513)

crypto/asn1/a_int.c

@@ -79,8 +79,14 @@ static void twos_complement(unsigned char *dst, const unsigned char *src,
     unsigned int carry = pad & 1;
 
     /* Begin at the end of the encoding */
-    dst += len;
-    src += len;
+    if (len != 0) {
+        /*
+         * if len == 0 then src/dst could be NULL, and this would be undefined
+         * behaviour.
+         */
+        dst += len;
+        src += len;
+    }
     /* two's complement value: ~value + 1 */
     while (len-- != 0) {
         *(--dst) = (unsigned char)(carry += *(--src) ^ pad);

crypto/bio/bss_mem.c

@@ -299,7 +299,7 @@ static long mem_ctrl(BIO *b, int cmd, long num, void *ptr)
         ret = (long)bm->length;
         if (ptr != NULL) {
             pptr = (char **)ptr;
-            *pptr = (char *)&(bm->data[0]);
+            *pptr = (char *)(bm->data);
         }
         break;
     case BIO_C_SET_BUF_MEM:

crypto/pem/pem_lib.c

@@ -917,18 +917,13 @@ err:
 int PEM_read_bio_ex(BIO *bp, char **name_out, char **header,
                     unsigned char **data, long *len_out, unsigned int flags)
 {
-    EVP_ENCODE_CTX *ctx = EVP_ENCODE_CTX_new();
+    EVP_ENCODE_CTX *ctx = NULL;
     const BIO_METHOD *bmeth;
     BIO *headerB = NULL, *dataB = NULL;
     char *name = NULL;
     int len, taillen, headerlen, ret = 0;
     BUF_MEM * buf_mem;
 
-    if (ctx == NULL) {
-        ERR_raise(ERR_LIB_PEM, ERR_R_MALLOC_FAILURE);
-        return 0;
-    }
-
     *len_out = 0;
     *name_out = *header = NULL;
     *data = NULL;
@@ -951,9 +946,20 @@ int PEM_read_bio_ex(BIO *bp, char **name_out, char **header,
     if (!get_header_and_data(bp, &headerB, &dataB, name, flags))
         goto end;
 
-    EVP_DecodeInit(ctx);
     BIO_get_mem_ptr(dataB, &buf_mem);
     len = buf_mem->length;
+
+    /* There was no data in the PEM file */
+    if (len == 0)
+        goto end;
+
+    ctx = EVP_ENCODE_CTX_new();
+    if (ctx == NULL) {
+        ERR_raise(ERR_LIB_PEM, ERR_R_MALLOC_FAILURE);
+        goto end;
+    }
+
+    EVP_DecodeInit(ctx);
     if (EVP_DecodeUpdate(ctx, (unsigned char*)buf_mem->data, &len,
                          (unsigned char*)buf_mem->data, len) < 0
             || EVP_DecodeFinal(ctx, (unsigned char*)&(buf_mem->data[len]),
@@ -964,9 +970,6 @@ int PEM_read_bio_ex(BIO *bp, char **name_out, char **header,
     len += taillen;
     buf_mem->length = len;
 
-    /* There was no data in the PEM file; avoid malloc(0). */
-    if (len == 0)
-        goto end;
     headerlen = BIO_get_mem_data(headerB, NULL);
     *header = pem_malloc(headerlen + 1, flags);
     *data = pem_malloc(len, flags);

providers/implementations/ciphers/cipher_aes_ocb.c

@@ -177,7 +177,8 @@ static int aes_ocb_block_update_internal(PROV_AES_OCB_CTX *ctx,
         }
         *bufsz = 0;
         outlint = AES_BLOCK_SIZE;
-        out += AES_BLOCK_SIZE;
+        if (out != NULL)
+            out += AES_BLOCK_SIZE;
     }
     if (nextblocks > 0) {
         outlint += nextblocks;

test/filterprov.c

@@ -167,7 +167,7 @@ int filter_provider_set_filter(int operation, const char *filterstr)
     if (globs->num_dispatch >= MAX_FILTERS)
         goto err;
 
-    for (name = filterstrtmp; !last; name = sep + 1) {
+    for (name = filterstrtmp; !last; name = (sep == NULL ? NULL : sep + 1)) {
         sep = strstr(name, ":");
         if (sep != NULL)
             *sep = '\0';

test/testutil/format_output.c

@@ -108,8 +108,10 @@ static void test_fail_string_common(const char *prefix, const char *file,
             if (diff && i > 0)
                 test_printf_stderr("%4s    %s\n", "", bdiff);
         }
-        m1 += n1;
-        m2 += n2;
+        if (m1 != NULL)
+            m1 += n1;
+        if (m2 != NULL)
+            m2 += n2;
         l1 -= n1;
         l2 -= n2;
         cnt += width;
@@ -497,8 +499,10 @@ static void test_fail_memory_common(const char *prefix, const char *file,
             if (diff && i > 0)
                 test_printf_stderr("%4s  %s\n", "", bdiff);
         }
-        m1 += n1;
-        m2 += n2;
+        if (m1 != NULL)
+            m1 += n1;
+        if (m2 != NULL)
+            m2 += n2;
         l1 -= n1;
         l2 -= n2;
         cnt += bytes;