netdev - Re: [PATCH]: SCTP length validation.

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Date:	Sun, 22 Jun 2008 12:32:32 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	vladislav.yasevich@...com
Cc:	netdev@...r.kernel.org, linux-sctp@...r.kernel.org
Subject: Re: [PATCH]: SCTP length validation.

From: Vlad Yasevich <vladislav.yasevich@...com>
Date: Sat, 21 Jun 2008 11:55:19 -0400

> The same vulnerability also exists in sctp_getsockopt_peer_addrs_old().
> It's a bit more difficult to trigger since there is a dependency on
> the peer being multihomed as well, but it's still possible to cause the
> overwrite.

I can't see how that's possible.  This case looks harmless to
me.

The kernel side accesses are perfectly protected.  The kernel
will only access the actual address list stored via:

	list_for_each_entry(from, &asoc->peer.transport_addr_list,
				transports) {
 ...
		cnt ++;
		if (cnt >= getaddrs.addr_num) break;
	}
	getaddrs.addr_num = cnt;

Copies are only made to userspace, and the given ->addr_num only
serves as an early break-out from that loop.  I mean, take a look,
those lines in the above are the only aaccesses made to the user's
provided addr_num value.

There is no possibility to use strange ->addr_num values
in order to read or write kernel memory outside of the
intended bounds.

I don't even see any value to adding new checks here.
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