net: gro: don't merge zcopy skbs

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: 753f1ca4e1e5 ("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>

diff --git a/net/core/gro.c b/net/core/gro.c
index 9f8960789b2cfbc397c944044af07ee167598ad1..a847539834679cd52938e3bf907a838b75811b08 100644 (file)
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -109,6 +109,9 @@ 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;
+
        if (unlikely(p->len + len >= netif_get_gro_max_size(p->dev, p) ||
                     NAPI_GRO_CB(skb)->flush))
                return -E2BIG;