netdev - Re: [PATCH net-next-2.6] filter: add a security check at install time

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Date:	Thu, 02 Dec 2010 14:14:01 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>, hagen@...u.net,
	wirelesser@...il.com, netdev@...r.kernel.org,
	Dan Rosenberg <drosenberg@...curity.com>
Subject: Re: [PATCH net-next-2.6] filter: add a security check at install
 time

Le jeudi 02 décembre 2010 à 19:29 +0800, Changli Gao a écrit :
> On Thu, Dec 2, 2010 at 7:15 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> > Their scratch memory is not on stack but part of the filter, so no
> > security problem (You can only read previous values of scratch registers
> > written by your own filter on handling a previous packet.)
> >
> 
> The code I checked is the newest in SVN. The scratch memory is really on stack.
> 

> u_int
> bpf_filter(const struct bpf_insn *pc, u_char *p, u_int wirelen, u_int buflen)
> {
>         u_int32_t A = 0, X = 0;
>         bpf_u_int32 k;
>         u_int32_t mem[BPF_MEMWORDS];
> 
> 
> 

This legacy code is not used on x86 now they have JIT by default ?

My remark about SMP 'problem' was about their JIT implementation.

net/bpf_jitter.h
/* Structure describing a native filtering program created by the jitter. */

typedef struct bpf_jit_filter {
        /* The native filtering binary, in the form of a bpf_filter_func. */
        bpf_filter_func func;

        int             mem[BPF_MEMWORDS];      /* Scratch memory */
} bpf_jit_filter;

Apparently they use locking around this stuff

BPFD_LOCK(d);
...
   bf = bpf_jitter_enable != 0 ? d->bd_bfilter : NULL;
   if (bf != NULL)
	slen = (*(bf->func))(pkt, pktlen, pktlen); 
   else
	slen = bpf_filter(d->bd_rfilter, pkt, pktlen, pktlen);

BPFD_UNLOCK(d);



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