[SRU][N][PATCH 1/1] net: gro: don't merge zcopy skbs

[Cengiz Can]

From: Sabrina Dubroca <sd at queasysnail.net>

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 at redhat.com>
Signed-off-by: Sabrina Dubroca <sd at queasysnail.net>
Reviewed-by: Willem de Bruijn <willemb at google.com>
Link: https://patch.msgid.link/c3b7f906bbfcbdfd7b4fa9d6c18a438870df85be.1779307748.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit 4db79a322db8c97f7b73b8a347395ef4d685eb40 netdev/net)
BugLink: https://bugs.launchpad.net/bugs/2154172
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 net/core/gro.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/gro.c b/net/core/gro.c
index 8d25274c4beb..155da53ce3be 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -110,6 +110,9 @@ 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;
-- 
2.43.0