Re: [iptables PATCH] extensions: string: Clarify description of --to

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

On Thu, Oct 12, 2023 at 06:08:42PM +0200, Phil Sutter wrote:
> String match indeed returns a match as long as the given pattern starts
> in the range of --from and --to, update the text accordingly.
> Also add a note regarding fragment boundaries.
>
> Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1707
> Signed-off-by: Phil Sutter <phil@nwl.cc>
> ---
>  extensions/libxt_string.man | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/extensions/libxt_string.man b/extensions/libxt_string.man
> index 2a470ece19c9d..efdda492ae78d 100644
> --- a/extensions/libxt_string.man
> +++ b/extensions/libxt_string.man
> @@ -7,9 +7,13 @@ Select the pattern matching strategy. (bm = Boyer-Moore, kmp = Knuth-Pratt-Morri
>  Set the offset from which it starts looking for any matching. If not passed, default is 0.
>  .TP
>  \fB\-\-to\fP \fIoffset\fP
> -Set the offset up to which should be scanned. That is, byte \fIoffset\fP-1
> -(counting from 0) is the last one that is scanned.
> +Set the offset up to which should be scanned. If the pattern does not start
> +within this offset, it is not considered a match.
>  If not passed, default is the packet size.
> +A second function of this parameter is instructing the kernel how much data
> +from the packet should be provided. With non-linear skbuffs (e.g. due to
> +fragmentation), a pattern extending past this offset may not be found. Also see
> +the related note below about Boyer-Moore algorithm in these cases.

Then, matching on:

- linear skbuff: if the pattern falls within from-to, all good.
- non-linear skbuff: if pattern falls within from-to, but remaining
  patter

This is clearly broken, the fix is just to document this?

No attempt to fix it this from the kernel?