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xen/netback: Fix buffer overrun triggered by unusual packet

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It is possible that a guest can send a packet that contains a head + 18
slots and yet has a len <= XEN_NETBACK_TX_COPY_LEN. This causes nr_slots
to underflow in xenvif_get_requests() which then causes the subsequent
loop's termination condition to be wrong, causing a buffer overrun of
queue->tx_map_ops.

Rework the code to account for the extra frag_overflow slots.

This is CVE-2023-34319 / XSA-432.

Fixes: ad7f402ae4 ("xen/netback: Ensure protocol headers don't fall in the non-linear area")
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Ross Lagerwall 2023-08-03 08:41:22 +02:00 committed by Juergen Gross
parent ec351c8f2e
commit 534fc31d09
1 changed files with 10 additions and 5 deletions
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15
drivers/net/xen-netback/netback.c
View file

@ -396,7 +396,7 @@ static void xenvif_get_requests(struct xenvif_queue *queue,
struct gnttab_map_grant_ref *gop = queue->tx_map_ops + *map_ops;
struct xen_netif_tx_request *txp = first;
nr_slots = shinfo->nr_frags + 1;
nr_slots = shinfo->nr_frags + frag_overflow + 1;
copy_count(skb) = 0;
XENVIF_TX_CB(skb)->split_mask = 0;
@ -462,8 +462,8 @@ static void xenvif_get_requests(struct xenvif_queue *queue,
}
}
for (shinfo->nr_frags = 0; shinfo->nr_frags < nr_slots;
shinfo->nr_frags++, gop++) {
for (shinfo->nr_frags = 0; nr_slots > 0 && shinfo->nr_frags < MAX_SKB_FRAGS;
shinfo->nr_frags++, gop++, nr_slots--) {
index = pending_index(queue->pending_cons++);
pending_idx = queue->pending_ring[index];
xenvif_tx_create_map_op(queue, pending_idx, txp,
@ -476,12 +476,12 @@ static void xenvif_get_requests(struct xenvif_queue *queue,
txp++;
}
if (frag_overflow) {
if (nr_slots > 0) {
shinfo = skb_shinfo(nskb);
frags = shinfo->frags;
for (shinfo->nr_frags = 0; shinfo->nr_frags < frag_overflow;
for (shinfo->nr_frags = 0; shinfo->nr_frags < nr_slots;
shinfo->nr_frags++, txp++, gop++) {
index = pending_index(queue->pending_cons++);
pending_idx = queue->pending_ring[index];
@ -492,6 +492,11 @@ static void xenvif_get_requests(struct xenvif_queue *queue,
}
skb_shinfo(skb)->frag_list = nskb;
} else if (nskb) {
/* A frag_list skb was allocated but it is no longer needed
* because enough slots were converted to copy ops above.
*/
kfree_skb(nskb);
}
(*copy_ops) = cop - queue->tx_copy_ops;