Streaming BIOs assume they can write to NULL BIOs

At least SMIME_text() relies on this. Pushing an error on the stack trips
PKCS7 regress in py-cryptography, so indicate nothing was written instead
of throwing an error.

Reported by Alex Gaynor a while back

ok jsing

1 files changed, 4 insertions, 5 deletions

diff --git a/src/lib/libcrypto/bio/bio_lib.c b/src/lib/libcrypto/bio/bio_lib.c
index 31b1e7305d..d14507884b 100644
--- a/src/lib/libcrypto/bio/bio_lib.c
+++ b/src/lib/libcrypto/bio/bio_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bio_lib.c,v 1.43 2022/12/16 13:41:55 schwarze Exp $ */
+/* $OpenBSD: bio_lib.c,v 1.44 2023/03/15 06:14:02 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -380,10 +380,9 @@ BIO_write(BIO *b, const void *in, int inl)
         size_t writebytes = 0;
         int ret;
 
-        if (b == NULL) {
-                BIOerror(ERR_R_PASSED_NULL_PARAMETER);
-                return (-1);
-        }
+        /* Not an error. Things like SMIME_text() assume that this succeeds. */
+        if (b == NULL)
+                return (0);
 
         if (inl <= 0)
                 return (0);