Fix read pipelining

During read pipelining we must ensure that the buffer is sufficiently large
to read enough data to fill our pipelines. We also remove some code that
moved data to the start of the packet if we can. This was unnecessary
because of later code which would end up moving it anyway. The earlier move
was also incorrect in the case that |clearold| was 0. This would cause the
read pipelining code to fail with sufficiently large records.

Fixes openssl#20197

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from openssl#20208)

ssl/record/rec_layer_s3.c

@@ -215,25 +215,7 @@ int ssl3_read_n(SSL *s, size_t n, size_t max, int extend, int clearold,
         /* start with empty packet ... */
         if (left == 0)
             rb->offset = align;
-        else if (align != 0 && left >= SSL3_RT_HEADER_LENGTH) {
-            /*
-             * check if next packet length is large enough to justify payload
-             * alignment...
-             */
-            pkt = rb->buf + rb->offset;
-            if (pkt[0] == SSL3_RT_APPLICATION_DATA
-                && (pkt[3] << 8 | pkt[4]) >= 128) {
-                /*
-                 * Note that even if packet is corrupted and its length field
-                 * is insane, we can only be led to wrong decision about
-                 * whether memmove will occur or not. Header values has no
-                 * effect on memmove arguments and therefore no buffer
-                 * overrun can be triggered.
-                 */
-                memmove(rb->buf + align, pkt, left);
-                rb->offset = align;
-            }
-        }
+
         s->rlayer.packet = rb->buf + rb->offset;
         s->rlayer.packet_length = 0;
         /* ... now we can act as if 'extend' was set */

ssl/record/ssl3_buffer.c

@@ -58,6 +58,11 @@ int ssl3_setup_read_buffer(SSL *s)
         if (ssl_allow_compression(s))
             len += SSL3_RT_MAX_COMPRESSED_OVERHEAD;
 #endif
+
+        /* Ensure our buffer is large enough to support all our pipelines */
+        if (s->max_pipelines > 1)
+            len *= s->max_pipelines;
+
         if (b->default_len > len)
             len = b->default_len;
         if ((p = OPENSSL_malloc(len)) == NULL) {