[PATCH 6.1 251/303] veth: convert frag_list skbs before running XDP

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matt Fleming <[email protected]>

[ Upstream commit d0d6415963040c401e7a7e4e482a698ba52448cb ]

A frag_list skb can reach veth with data_len set but nr_frags zero.
veth_convert_skb_to_xdp_buff() only converts skbs that are shared,
locked, have frags[], or do not have enough headroom. It later uses
skb_is_nonlinear() to decide whether to set XDP_FLAGS_HAS_FRAGS and
xdp_frags_size.

That exposes frag_list data to XDP as if it were stored in frags[], but
frags[] is empty. AF_XDP copy mode can then trust the bogus XDP fragment
metadata, walk an empty fragment entry, and crash in memcpy() from
__xsk_rcv().

Route non-linear skbs through skb_pp_cow_data() before exposing them to
XDP, and only advertise XDP frags when the resulting skb has frags[].
skb_copy_bits() already handles frag_list input, and skb_pp_cow_data()
builds frags[] output with skb_add_rx_frag(), which is the
representation XDP multi-buffer expects.

Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb")
Cc: [email protected]
Signed-off-by: Matt Fleming <[email protected]>
Reviewed-by: Toke Høiland-Jørgensen <[email protected]>
Acked-by: Lorenzo Bianconi <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/veth.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -695,7 +695,7 @@ static int veth_convert_skb_to_xdp_buff(
 	u32 frame_sz;
 
 	if (skb_shared(skb) || skb_head_is_locked(skb) ||
-	    skb_shinfo(skb)->nr_frags ||
+	    skb_is_nonlinear(skb) ||
 	    skb_headroom(skb) < XDP_PACKET_HEADROOM) {
 		u32 size, len, max_head_size, off;
 		struct sk_buff *nskb;
@@ -770,7 +770,7 @@ static int veth_convert_skb_to_xdp_buff(
 	xdp_prepare_buff(xdp, skb->head, skb_headroom(skb),
 			 skb_headlen(skb), true);
 
-	if (skb_is_nonlinear(skb)) {
+	if (skb_shinfo(skb)->nr_frags) {
 		skb_shinfo(skb)->xdp_frags_size = skb->data_len;
 		xdp_buff_set_frags_flag(xdp);
 	} else {