BUG/MAJOR: buffer: check the space left is enough or not when input data in a buffer is wrapped

HAProxy will crash with the following configuration:

global
    ...
    tune.bufsize 1024
    tune.maxrewrite 0
frontend xxx
    ...
backend  yyy
   ...
   cookie cookie insert maxidle 300s

If client sends a request of which object size is more than tune.bufsize (1024
bytes), HAProxy will crash.

After doing some debugging, the crash was caused by http_header_add_tail2() ->
buffer_insert_line2() while inserting cookie at the end of response header.
Part codes of buffer_insert_line2() are as below:

int buffer_insert_line2(struct buffer *b, char *pos, const char *str, int len)
{
    int delta;

    delta = len + 2;

    if (bi_end(b) + delta >= b->data + b->size)
        return 0;  /* no space left */

    /* first, protect the end of the buffer */
    memmove(pos + delta, pos, bi_end(b) - pos);
    ...
}

Since tune.maxrewrite is 0, HAProxy can receive 1024 bytes once which is equals
to full buffer size.  Under such condition, the buffer is full and bi_end(b)
will be wrapped to the start of buffer which pointed to b->data. As a result,
though there is no space left in buffer, the check condition
	if (bi_end(b) + delta >= b->data + b->size)
will be true, then memmove() is called, and (pos + delta) will exceed the end
of buffer (b->data + b->size), HAProxy crashes

Just take buffer_replace2() as a reference, the other check when input data in
a buffer is wrapped should be also added into buffer_insert_line2().

This fix must be backported to 1.5.

Signed-off-by: Godbach <nylzhaowei@gmail.com>
(cherry picked from commit a6547c1338ab139332a66096d449e7ac1a56a591)

src/buffer.c

@@ -88,6 +88,11 @@ int buffer_insert_line2(struct buffer *b, char *pos, const char *str, int len)
 	if (bi_end(b) + delta >= b->data + b->size)
 		return 0;  /* no space left */
 
+	if (buffer_not_empty(b) &&
+	    bi_end(b) + delta > bo_ptr(b) &&
+	    bo_ptr(b) >= bi_end(b))
+		return 0;  /* no space left before wrapping data */
+
 	/* first, protect the end of the buffer */
 	memmove(pos + delta, pos, bi_end(b) - pos);