BIO_f_zlib: Properly handle BIO_CTRL_PENDING and BIO_CTRL_WPENDING calls.

There can be data to write in output buffer and data to read that were
not yet read in the input stream.

Fixes #9866

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9877)

(cherry picked from commit 6beb8b39ba8e4cb005c1fcd2586ba19e17f04b95)

1 files changed, 22 insertions, 0 deletions

diff --git a/crypto/comp/c_zlib.c b/crypto/comp/c_zlib.c
index d688deee5f..7c1be358fd 100644
--- a/crypto/comp/c_zlib.c
+++ b/crypto/comp/c_zlib.c
@@ -598,6 +598,28 @@ static long bio_zlib_ctrl(BIO *b, int cmd, long num, void *ptr)
         BIO_copy_next_retry(b);
         break;
 
+    case BIO_CTRL_WPENDING:
+        if (ctx->obuf == NULL)
+            return 0;
+
+        if (ctx->odone) {
+            ret = ctx->ocount;
+        } else {
+            ret = ctx->ocount;
+            if (ret == 0)
+                /* Unknown amount pending but we are not finished */
+                ret = 1;
+        }
+        if (ret == 0)
+            ret = BIO_ctrl(next, cmd, num, ptr);
+        break;
+
+    case BIO_CTRL_PENDING:
+        ret = ctx->zin.avail_in;
+        if (ret == 0)
+            ret = BIO_ctrl(next, cmd, num, ptr);
+        break;
+
     default:
         ret = BIO_ctrl(next, cmd, num, ptr);
         break;