[lkml]   [2004]   [Nov]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [BK PATCH] Fix ip_conntrack_amanda data corruption bug that breaks amanda dumps
Matthias Andree wrote:

>On Thu, 04 Nov 2004, Patrick McHardy wrote:
>>- data = amp;
>>- data_limit = amp + skb->len - dataoff;
>>+ skb_copy_bits(skb, dataoff, amanda_buffer, skb->len - dataoff);
>>+ data = amanda_buffer;
>>+ data_limit = amanda_buffer + skb->len - dataoff;
>Does this mean the whole buffer is still copied?

>If so: Making a local copy of the packet just to be able to stuff NUL
>bytes to suit or "optimize" strstr functions is plain nonsense - amanda
>pipes several GByte through the kernel at each run, and copying
>gazillions of bits around, wasting millions of CPU cycles, just because
>someone is too lazy to spell a more decent search function, is
>bad design.
This is just the UDP control connection, the data is not copied
or scanned. Feel free to send a patch that doesn't need to
copy linear skbs and doesn't need to modify the skb.

>Same consideration applies to FTP connection tracking.
>I wrote a memstr function for bogofilter (GPL v2) that we could use
>inside the kernel, as a length-limited strstr replacement, as in "search
>the first buffer_size bytes starting with buffer_base for the first
>occurrence of const char *needle". That avoids all buffer modifications
>in ip_conntrack_amanda.c AFAICS. It's also slow because it does a linear
>search and not an optimized search as the sophisticated KMP and other
>search algorithms would be able to do, but then again the generic strstr
>inside the kernel is linear, too.
non-linear skb have fragments scattered in memory, you have to
copy them or scan with a function that is aware of how the data
is layed out in memory. Look at Harald's notes from the netfilter
workshop for details on current work in this area.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 14:07    [from the cache]
©2003-2014 Jasper Spaans. hosted at Digital Ocean