Re: [Libevent-users] [PATCH] evbuffer_search_range fails when searching the last byte

[Nir Soffer <nirsof@xxxxxxxxx>]

On Jun 7, 2011, at 4:03 AM, Nick Mathewson wrote:

> On Mon, Jun 6, 2011 at 8:37 PM, Nir Soffer <nirsof@xxxxxxxxx> wrote:
> Here's another patch that might make stuff work.  Before I'd apply it,
> I'd like to have a look through everything that's using
> evbuffer_ptr_set() and evbuffer_ptr right now to make sure that
> nothing will freak out if it gets a pointer like this.
>
> What do you think?

Here is a new test case that fail with this patch:

    /* Search the next 18 bytes for "attack" */
    tt_int_op(evbuffer_ptr_set(buf, &end, 18, EVBUFFER_PTR_SET), ==,  
0);
    pos = evbuffer_search_range(buf, "attack", 6, NULL, &end);
    tt_int_op(pos.pos, ==, 11);

The use case is simple - I want to limit the search to some range,  
which happen to be longer then the buffer. To make this work with this  
patch, I have to do something like this:

	size_t length = evbuffer_get_length(buf);

	if (limit > length)
		limit = length;
		
	evbuffer_ptr_set(buf, &end, limit, EVBUFFER_PTR_SET);
	pos = evbuffer_search_range(buf, "needle", 6, NULL, &end);

But what I would like to do is this:

	evbuffer_ptr_set(buf, &end, limit, EVBUFFER_PTR_SET);
	pos = evbuffer_search_range(buf, "needle", 6, NULL, &end);

So evebuffer_ptr_set should succeed even if position is after the end  
of the buffer;

The attached patch make it work, but accepting any position, even if  
it out of the buffer range.

I did not inspect the code handling these ranges yet - it is possible  
that such ranges will lead to accessing memory you should not access,  
if the code was depending on ranges to be always within the buffer.

Attachment: 0003-Allow-evbuffer_ptr-to-point-after-the-buffer-content.patch
Description: Binary data