From: Willem de Bruijn <willemb@xxxxxxxxxx> [ Upstream commit 8d21e9963bec1aad2280cdd034c8993033ef2948 ] GRE with TUNNEL_CSUM will apply local checksum offload on CHECKSUM_PARTIAL packets. ipgre_xmit must validate csum_start after an optional skb_pull, else lco_csum may trigger an overflow. The original check was if (csum && skb_checksum_start(skb) < skb->data) return -EINVAL; This had false positives when skb_checksum_start is undefined: when ip_summed is not CHECKSUM_PARTIAL. A discussed refinement was straightforward if (csum && skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_start(skb) < skb->data) return -EINVAL; But was eventually revised more thoroughly: - restrict the check to the only branch where needed, in an uncommon GRE path that uses header_ops and calls skb_pull. - test skb_transport_header, which is set along with csum_start in skb_partial_csum_set in the normal header_ops datapath. Turns out skbs can arrive in this branch without the transport header set, e.g., through BPF redirection. Revise the check back to check csum_start directly, and only if CHECKSUM_PARTIAL. Do leave the check in the updated location. Check field regardless of whether TUNNEL_CSUM is configured. Link: https://lore.kernel.org/netdev/YS+h%2FtqCJJiQei+W@shredder/ Link: https://lore.kernel.org/all/20210902193447.94039-2-willemdebruijn.kernel@xxxxxxxxx/T/#u Fixes: 8a0ed250f911 ("ip_gre: validate csum_start only on pull") Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx> Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx> Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx> Link: https://lore.kernel.org/r/20220606132107.3582565-1-willemdebruijn.kernel@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- net/ipv4/ip_gre.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index 2a80038575d2..a7e32be8714f 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -624,21 +624,20 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb, } if (dev->header_ops) { - const int pull_len = tunnel->hlen + sizeof(struct iphdr); - if (skb_cow_head(skb, 0)) goto free_skb; tnl_params = (const struct iphdr *)skb->data; - if (pull_len > skb_transport_offset(skb)) - goto free_skb; - /* Pull skb since ip_tunnel_xmit() needs skb->data pointing * to gre header. */ - skb_pull(skb, pull_len); + skb_pull(skb, tunnel->hlen + sizeof(struct iphdr)); skb_reset_mac_header(skb); + + if (skb->ip_summed == CHECKSUM_PARTIAL && + skb_checksum_start(skb) < skb->data) + goto free_skb; } else { if (skb_cow_head(skb, dev->needed_headroom)) goto free_skb; -- 2.35.1
