[openssl] OpenSSL_1_1_1-stable update

[Richard Levitte]

The branch OpenSSL_1_1_1-stable has been updated
       via  525e2288fafd76e416b4a6dad6d95d8b598f8152 (commit)
      from  cd5acbb47518b8abf9030ace7ad6db9e02d6b968 (commit)


- Log -----------------------------------------------------------------
commit 525e2288fafd76e416b4a6dad6d95d8b598f8152
Author: Richard Levitte <levitte at openssl.org>
Date:   Sun Jan 19 03:19:31 2020 +0100

    DOC: document in more detail what a BIO_read_ex() via BIO_f_buffer() does
    
    The BIO_f_buffer() documentation tells in enough detail how it affects
    BIO_gets(), but not how it affects BIO_read_ex().  This change
    remedies that.
    
    Fixes #10859
    
    Reviewed-by: Tim Hudson <tjh at openssl.org>
    (Merged from https://github.com/openssl/openssl/pull/10890)
    
    (cherry picked from commit 9a4fd80ee0ad1833879b6a55c9c4673eeb8446a3)

-----------------------------------------------------------------------

Summary of changes:
 doc/man3/BIO_f_buffer.pod | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/doc/man3/BIO_f_buffer.pod b/doc/man3/BIO_f_buffer.pod
index 8ceaaa3c03..80733e2be2 100644
--- a/doc/man3/BIO_f_buffer.pod
+++ b/doc/man3/BIO_f_buffer.pod
@@ -49,10 +49,20 @@ is expanded.
 
 These functions, other than BIO_f_buffer(), are implemented as macros.
 
-Buffering BIOs implement BIO_gets() by using BIO_read_ex() operations on the
-next BIO in the chain. By prepending a buffering BIO to a chain it is therefore
-possible to provide BIO_gets() functionality if the following BIOs do not
-support it (for example SSL BIOs).
+Buffering BIOs implement BIO_read_ex() and BIO_gets() by using
+BIO_read_ex() operations on the next BIO in the chain and storing the
+result in an internal buffer, from which bytes are given back to the
+caller as appropriate for the call; a BIO_gets() is guaranteed to give
+the caller a whole line, and BIO_read_ex() is guaranteed to give the
+caller the number of bytes it asks for, unless there's an error or end
+of communication is reached in the next BIO.  By prepending a
+buffering BIO to a chain it is therefore possible to provide
+BIO_gets() or exact size BIO_read_ex() functionality if the following
+BIOs do not support it.
+
+Do not add more than one BIO_f_buffer() to a BIO chain.  The result of
+doing so will force a full read of the size of the internal buffer of
+the top BIO_f_buffer(), which is 4 KiB at a minimum.
 
 Data is only written to the next BIO in the chain when the write buffer fills
 or when BIO_flush() is called. It is therefore important to call BIO_flush()