xen-netback: don't produce zero-size SKB frags
commit c7ec4f2d684e17d69bbdd7c4324db0ef5daac26a upstream.
While frontends may submit zero-size requests (wasting a precious slot),
core networking code as of at least 3ece782693c4b ("sock: skb_copy_ubufs
support for compound pages") can't deal with SKBs when they have all
zero-size fragments. Respond to empty requests right when populating
fragments; all further processing is fragment based and hence won't
encounter these empty requests anymore.
In a way this should have been that way from the beginning: When no data
is to be transferred for a particular request, there's not even a point
in validating the respective grant ref. That's no different from e.g.
passing NULL into memcpy() when at the same time the size is 0.
This is XSA-448 / CVE-2023-46838.
BUG=b/323501498
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2023-46838 in the Linux kernel.
Change-Id: I9589596c21182df5219dffd37055fbc0dc986e57
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/64610
Reviewed-by: Michael Kochera <kochera@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 1c366dd..d25bb5b 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -463,12 +463,25 @@
}
for (shinfo->nr_frags = 0; nr_slots > 0 && shinfo->nr_frags < MAX_SKB_FRAGS;
- shinfo->nr_frags++, gop++, nr_slots--) {
+ nr_slots--) {
+ if (unlikely(!txp->size)) {
+ unsigned long flags;
+
+ spin_lock_irqsave(&queue->response_lock, flags);
+ make_tx_response(queue, txp, 0, XEN_NETIF_RSP_OKAY);
+ push_tx_responses(queue);
+ spin_unlock_irqrestore(&queue->response_lock, flags);
+ ++txp;
+ continue;
+ }
+
index = pending_index(queue->pending_cons++);
pending_idx = queue->pending_ring[index];
xenvif_tx_create_map_op(queue, pending_idx, txp,
txp == first ? extra_count : 0, gop);
frag_set_pending_idx(&frags[shinfo->nr_frags], pending_idx);
+ ++shinfo->nr_frags;
+ ++gop;
if (txp == first)
txp = txfrags;
@@ -481,20 +494,39 @@
shinfo = skb_shinfo(nskb);
frags = shinfo->frags;
- for (shinfo->nr_frags = 0; shinfo->nr_frags < nr_slots;
- shinfo->nr_frags++, txp++, gop++) {
+ for (shinfo->nr_frags = 0; shinfo->nr_frags < nr_slots; ++txp) {
+ if (unlikely(!txp->size)) {
+ unsigned long flags;
+
+ spin_lock_irqsave(&queue->response_lock, flags);
+ make_tx_response(queue, txp, 0,
+ XEN_NETIF_RSP_OKAY);
+ push_tx_responses(queue);
+ spin_unlock_irqrestore(&queue->response_lock,
+ flags);
+ continue;
+ }
+
index = pending_index(queue->pending_cons++);
pending_idx = queue->pending_ring[index];
xenvif_tx_create_map_op(queue, pending_idx, txp, 0,
gop);
frag_set_pending_idx(&frags[shinfo->nr_frags],
pending_idx);
+ ++shinfo->nr_frags;
+ ++gop;
}
- skb_shinfo(skb)->frag_list = nskb;
- } else if (nskb) {
+ if (shinfo->nr_frags) {
+ skb_shinfo(skb)->frag_list = nskb;
+ nskb = NULL;
+ }
+ }
+
+ if (nskb) {
/* A frag_list skb was allocated but it is no longer needed
- * because enough slots were converted to copy ops above.
+ * because enough slots were converted to copy ops above or some
+ * were empty.
*/
kfree_skb(nskb);
}
