Re: [PATCH nf v2] lib/ts_bm: reset initial match offset for every block of text

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, Jun 19, 2023 at 08:06:57PM +0100, Jeremy Sowden wrote:
> The `shift` variable which indicates the offset in the string at which
> to start matching the pattern is initialized to `bm->patlen - 1`, but it
> is not reset when a new block is retrieved.  This means the implemen-
> tation may start looking at later and later positions in each successive
> block and miss occurrences of the pattern at the beginning.  E.g.,
> consider a HTTP packet held in a non-linear skb, where the HTTP request
> line occurs in the second block:
> 
>   [... 52 bytes of packet headers ...]
>   GET /bmtest HTTP/1.1\r\nHost: www.example.com\r\n\r\n
> 
> and the pattern is "GET /bmtest".
> 
> Once the first block comprising the packet headers has been examined,
> `shift` will be pointing to somewhere near the end of the block, and so
> when the second block is examined the request line at the beginning will
> be missed.
> 
> Reinitialize the variable for each new block.

Applied to nf.git, thanks