Re: [PATCH]: SCTP length validation.

David Miller wrote:

From: Vlad Yasevich <redacted>
Date: Sat, 21 Jun 2008 11:55:19 -0400

quoted

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.

You are right.  I didn't look far enough.  Since there is no kmalloc(),
the overflow of kernel memory is not possible, and copy_to_user should
take care of any overflows of the user memory.

-vlad