Improve the implementation of BIO_push(3) such that it changes nothing

and reports failure if a call would result in a cycle.
The algorithm used was originally suggested by jsing@.
Feedback and OK tb@.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bio/bio_lib.c b/src/lib/libcrypto/bio/bio_lib.c
index 4c3d7ed5f5..3eb0869ca9 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 1.41 2022/12/06 17:59:21 schwarze Exp $ */
+/* $OpenBSD: bio_lib.c,v 1.42 2022/12/07 23:08:47 schwarze Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -637,6 +637,12 @@ BIO_push(BIO *b, BIO *bio)
 
         if (b == NULL)
                 return (bio);
+
+        /* If this would create a cycle, change nothing and fail. */
+        for (lb = bio; lb != NULL; lb = lb->next_bio)
+                if (lb == b)
+                        return NULL;
+
         lb = b;
         while (lb->next_bio != NULL)
                 lb = lb->next_bio;