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Date: Fri, 04 Apr 2008 08:24:12 -0400
From: jamal <hadi@...erus.ca>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org, joern@...ybastard.org,
herbert@...dor.apana.org.au, Paul Moore <paul.moore@...com>,
James Morris <jmorris@...ei.org>
Subject: Re: speaking of stacks
On Thu, 2008-03-04 at 14:18 -0700, David Miller wrote:
> You probably have most of the security infrastructure turned
> off, therefore GCC can see that 'tmp' is basically unused
> and can therefore be totally eliminated.
>
> The memset() call makes 'tmp' get passed by reference to
> another function, and thus become used.
Indeed, thanks - that resolves the mystery;->
Testing by moving the tmp memseting inside security_xfrm_policy_alloc()
so memset is only invoked when CONFIG_SECURITY_NETWORK_XFRM resolves the
stack abuse.
BTW, of the top 10 stack abusers _in the kernel_ (should say based on my
config) constitute 3-4 spots which are caused by this exact thing.
I could send a patch that resolves the issue by moving memset but that
would only fix it for people like myself who turn off SELinux.
> This whole song and dance here is for SELINUX to set only
> the policy->security, so that we can pass that back down
> into the subsequent xfrm_policy_bysel_ctx().
>
> The thing to do is to rearrange these security layer hooks
> so that they take a "struct xfrm_sec_ctx **" instead of
> a full policy pointer.
>
> Then the code would look like:
>
> struct nlattr *rt = attrs[XFRMA_SEC_CTX];
> struct xfrm_sec_ctx *ctx;
>
> err = verify_sec_ctx_len(attrs);
> if (err)
> return err;
>
> if (rt) {
> struct xfrm_user_sec_ctx *uctx = nla_data(rt);
>
> if ((err = security_xfrm_policy_alloc(&ctx, uctx)))
> return err;
> }
> xp = xfrm_policy_bysel_ctx(type, p->dir, &p->sel, ctx,
> delete, &err);
> security_xfrm_policy_free(ctx);
>
> And thus the xfrm_policy wouldn't need to be on the stack
> any longer.
Yes, that would be cleaner than what i did; i will give the opportunity
to the SELinux folks to take a first crack at it with the above
approach.
CCing some of the SElinux folks.
Thanks Dave.
cheers,
jamal
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