Create bm->buf from the start to avoid arithmetic on NULL

This is a different way of avoiding the pointer arithmetic on NULL and
avoids test breakage in pyca/cryptography. This is also a gross hack
that penalizes existing callers of BIO_s_mem(), but this is rarely
called in a hot loop and if so that will most likely be a test.

ok kenjiro joshua jsing

1 files changed, 7 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bio/bss_mem.c b/src/lib/libcrypto/bio/bss_mem.c
index 0936ab4e83..f977a123a7 100644
--- a/src/lib/libcrypto/bio/bss_mem.c
+++ b/src/lib/libcrypto/bio/bss_mem.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bss_mem.c,v 1.25 2025/05/24 19:43:09 tb Exp $ */
+/* $OpenBSD: bss_mem.c,v 1.26 2025/05/24 19:45:34 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -162,6 +162,12 @@ mem_new(BIO *bio)
                 free(bm);
                 return 0;
         }
+        if (BUF_MEM_grow_clean(bm->buf, 64) != 64) {
+                BUF_MEM_free(bm->buf);
+                free(bm);
+                return 0;
+        }
+        bm->buf->length = 0;
 
         bio->shutdown = 1;
         bio->init = 1;