From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54083) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WUjWg-0001yT-Pj for qemu-devel@nongnu.org; Mon, 31 Mar 2014 17:14:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WUjWH-0007mk-Pi for qemu-devel@nongnu.org; Mon, 31 Mar 2014 17:13:50 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:65370) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WUjWH-0007m9-Fk for qemu-devel@nongnu.org; Mon, 31 Mar 2014 17:13:25 -0400 Received: by mail-lb0-f174.google.com with SMTP id u14so6193810lbd.5 for ; Mon, 31 Mar 2014 14:13:24 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20140331204900.GC12403@redhat.com> References: <1396275242-10810-1-git-send-email-mst@redhat.com> <1396275242-10810-14-git-send-email-mst@redhat.com> <20140331171122.GG11125@work-vm> <20140331204900.GC12403@redhat.com> From: Peter Maydell Date: Mon, 31 Mar 2014 22:13:04 +0100 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [PATCH v4 13/30] stellaris_enet: avoid buffer overrun on incoming migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Michael Roth , qemu-stable , "Dr. David Alan Gilbert" , QEMU Developers On 31 March 2014 21:49, Michael S. Tsirkin wrote: > On Mon, Mar 31, 2014 at 06:11:22PM +0100, Dr. David Alan Gilbert wrote: >> * Michael S. Tsirkin (mst@redhat.com) wrote: >> > CVE-2013-4532 >> > >> > s->next_packet is read from wire as an index into s->rx[]. If >> > s->next_packet exceeds the length of s->rx[], the buffer can be >> > subsequently overrun with arbitrary data from the wire. >> > >> > Fix this by failing migration if s->next_packet we read from >> > the wire exceeds this. >> > >> > Similarly, validate rx_fifo against sizeof(s->rx[].data). >> > >> > Finally, constrain rx len to a sensibly small positive >> > value, to avoid integer overruns when data model >> > later uses this value. >> > >> > Reported-by: Michael Roth >> > Reported-by: Peter Maydell >> > Signed-off-by: Michael S. Tsirkin >> > --- >> > hw/net/stellaris_enet.c | 24 ++++++++++++++++++++---- >> > 1 file changed, 20 insertions(+), 4 deletions(-) >> > >> > diff --git a/hw/net/stellaris_enet.c b/hw/net/stellaris_enet.c >> > index d04e6a4..182fd3e 100644 >> > --- a/hw/net/stellaris_enet.c >> > +++ b/hw/net/stellaris_enet.c >> > @@ -358,7 +358,7 @@ static void stellaris_enet_save(QEMUFile *f, void *opaque) >> > static int stellaris_enet_load(QEMUFile *f, void *opaque, int version_id) >> > { >> > stellaris_enet_state *s = (stellaris_enet_state *)opaque; >> > - int i; >> > + int i, v; >> > >> > if (version_id != 1) >> > return -EINVAL; >> > @@ -381,9 +381,25 @@ static int stellaris_enet_load(QEMUFile *f, void *opaque, int version_id) >> > qemu_get_buffer(f, s->rx[i].data, sizeof(s->rx[i].data)); >> > >> > } >> >> The loop that's just off the top here is: >> for (i = 0; i < 31; i++) { >> s->rx[i].len = qemu_get_be32(f); >> qemu_get_buffer(f, s->rx[i].data, sizeof(s->rx[i].data)); >> >> } >> >> Doesn't that 'len' need validating? I assume it's the size of the >> packet in the fixed sized buffer? (??) > > Not that I see where it's used as such. In the DATA case of stellaris_enet_read() -- when the current rx_fifo_len goes to zero we will uncritically set rx_fifo_len to s->rx[s->next_packet].len. So we must validate that it's between 0 and 2048 (the size of the rx[].data array), otherwise further reads from DATA will be able to run off the end of the data array for the following packet. >> > - s->next_packet = qemu_get_be32(f); >> > - s->rx_fifo = s->rx[s->next_packet].data + qemu_get_be32(f); >> > - s->rx_fifo_len = qemu_get_be32(f); >> > + v = qemu_get_be32(f); >> > + if (v < 0 || v >= ARRAY_SIZE(s->rx)) { >> > + return -EINVAL; >> > + } >> > + s->next_packet = v; >> > + v = qemu_get_be32(f); >> > + if (v < 0 || v >= sizeof(s->rx[i].data)) { >> > + return -EINVAL; >> > + } >> > + s->rx_fifo = s->rx[s->next_packet].data + v; >> > + v = qemu_get_be32(f); >> > + /* Set limit low enough to avoid integer overflow when >> > + * we do math on len later, but high enough to avoid >> > + * truncating any packets. >> > + */ >> > + if (v < 0 || v >= 0x100000) { >> > + return -EINVAL; >> > + } >> > + s->rx_fifo_len = v; >> >> I don't understand this - isn't the requirement that rx_fifo+rx_fifo_len be within >> the buffer (or I think it might be legal for the sum to point to the byte after the >> buffer)? >> My (quick first ever look at this code) reading is that rx_fifo and rx_fifo_len >> related to the current packet in-flight; although I've not quite convinced myself >> about what is supposed to happen at the end of the packet (which is why >> I say rx_fifo might point just at? the end. > Actually I forgot why I wrote this last check. > Peter said we should and I thought I see the issue ... > But I no longer see what kind of damage can rx_fifo_len cause > unless validated. Again, look at the DATA read logic. Every time the guest does a DATA read, we read from the four bytes at s->rx_fifo, increment rx_fifo by 4 and decrement rx_fifo_len by 4. When rx_fifo_len eventually goes to zero we will (on the subsequent read) reset both rx_fifo and rx_fifo_len from the next packet in the rx queue. So if the incoming data sets rx_fifo_len to (let us say) 0x10000, then the guest can cause us to read well off the end of the rx data array. This means your check isn't tight enough -- we need to ensure that rx_fifo and rx_fifo_len between them define a window into the rx data and nowhere else. As David says this means you need: v1 = qemu_get_be32(f); if (v1 < 0 || v1 > sizeof(s->rx[i].data)) { return -EINVAL; } s->rx_fifo = s->rx[s->next_packet].data + v1; v2 = qemu_get_be32(f); if (v2 < 0 || v1 + v2 > sizeof(s->rx[i].data)) { return -EINVAL; } s->rx_fifo_len = v2; The max check on v1 is actually only there to ensure that we don't have to think about integer overflow when we do the upper-bound check on v1 + v2. Note that v1 == sizeof(array) is OK if (and only if) v2 == 0. An assert in stellaris_enet_receive() that the net code never hands us a packet we can't fit in the array wouldn't go amiss either, but that's a separate issue. thanks -- PMM