netdev - Re: [Security] TIPC security issues

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Date:	Thu, 28 Oct 2010 08:32:37 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>,
	Andy Grover <andy.grover@...cle.com>
Cc:	jon.maloy@...csson.com, netdev@...r.kernel.org,
	drosenberg@...curity.com, security@...nel.org,
	allan.stephens@...driver.com
Subject: Re: [Security] TIPC security issues

Heh. We apparently have _another_ iovec overflow in networking. This time rds.

Reported by Thomas Pollet <thomas.pollet@...il.com>: look at
net/rds/rdma.c around line 490. It doesn't use the regular iovec code,
instead it cooks its own, and has a few problems with overflow.

It gathers the number of pages into an "unsigned int", and for each
entry in its own rds_iovec it will check that the size is < UINT_MAX,
and then generate the number of pages for that entry. With the whole
"unaligned address adds one" logic, it means that each entry can get
(UINT_MAX >> PAGE_SHIFT)+1 pages.

And how many entries can we have? Apparently that is capped to
UINT_MAX too. So add all those up, and they can easily overflow the
unsigned int page counter.

So this time fixing verify_iovec() doesn't help, because rds just
cooks its own, and this is using a totally different interface: it
seems to hook into sendmsg, but it looks like it uses the ancillary
data objects and passes in its own magical iovec rather than use any
"normal" iovec thing. I don't know the code, I may be totally off.

Attached is a half-arsed patch. I say "half-arsed" because I think it
fixes one thing, but I haven't looked at any other use. And quite
frankly, even the one thing it fixes is totally broken: the iovec is
left in user space, so there are all those crazy race-conditions where
another thread in user space can _change_ the rds_iovec after we have
counted the pages, and now the page count is totally wrong.

So the code is just an unmitigated disaster from any standpoint. My
patch - if it works - makes it slightly better. But I'd suggest
disabling RDS in any sane setup.

This was the same subsystem that totally didn't check the user
addresses at all, after all. So there are probably tons of other bugs
lurking.

Btw: patch is totally untested. I haven't even compiled it. So take it
with a pinch of salt.

                                                 Linus

View attachment "patch.diff" of type "text/x-patch" (1306 bytes)