net: gro: don't merge zcopy skbs

cve CVE-Pending
commit-author Sabrina Dubroca <sd@queasysnail.net>
commit 4db79a3
upstream-diff |
  Context conflict in net/core/gro.c: 5.14 uses a local gro_max_size
  variable lookup instead of upstream's netif_get_gro_max_size() helper.
  The skb_zcopy() check was added at the same location, before the
  gro_max_size lookup. Functionally identical to upstream.

skb_gro_receive() can currently copy frags between the source and GRO
skb, without checking the zerocopy status, and in particular the
SKBFL_MANAGED_FRAG_REFS flag.

When SKBFL_MANAGED_FRAG_REFS is set, the skb doesn't hold a reference
on the pages in shinfo->frags. Appending those frags to another skb's
frags without fixing up the page refcount can lead to UAF.

When either the last skb in the GRO chain (the one we would append
frags to) or the source skb is zerocopy, don't merge the skbs.

Fixes: 753f1ca ("net: introduce managed frags infrastructure")
Reported-by: Huzaifa Sidhpurwala <huzaifas@redhat.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/c3b7f906bbfcbdfd7b4fa9d6c18a438870df85be.1779307748.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Shreeya Patel <spatel@ciq.com>

Author: qsn

net/core/gro.c

@@ -113,6 +113,9 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 	if (p->pp_recycle != skb->pp_recycle)
 		return -ETOOMANYREFS;
 
+	if (skb_zcopy(p) || skb_zcopy(skb))
+		return -ETOOMANYREFS;
+
 	/* pairs with WRITE_ONCE() in netif_set_gro(_ipv4)_max_size() */
 	gro_max_size = p->protocol == htons(ETH_P_IPV6) ?
 			READ_ONCE(p->dev->gro_max_size) :