Revert bio_prev removal

As schwarze points out, you can pop any BIO in a chain, not just the first
one (bonus points for a great name for this API).

The internal doubly linked was used to fix up the BIO chain bio was part
of when you BIO_pop() a bio that wasn't in the first position, which is
explicitly allowed in our documentation and implied by OpenSSL's.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bio/bio_local.h b/src/lib/libcrypto/bio/bio_local.h
index 94dd460bc5..4eecf7e04a 100644
--- a/src/lib/libcrypto/bio/bio_local.h
+++ b/src/lib/libcrypto/bio/bio_local.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: bio_local.h,v 1.4 2022/11/28 07:50:00 tb Exp $ */
+/* $OpenBSD: bio_local.h,v 1.5 2022/12/02 19:44:04 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -87,6 +87,7 @@ struct bio_st {
         int num;
         void *ptr;
         struct bio_st *next_bio;        /* used by filter BIOs */
+        struct bio_st *prev_bio;        /* used by filter BIOs */
         int references;
         unsigned long num_read;
         unsigned long num_write;