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authorWillem de Bruijn <willemb@google.com>2022-06-06 09:21:07 -0400
committerJakub Kicinski <kuba@kernel.org>2022-06-08 20:34:43 -0700
commit8d21e9963bec1aad2280cdd034c8993033ef2948 (patch)
tree7ebe3eb38c30a7360c49d665f062708ac301fea0 /net
parentd5d4c36398ba66c033602b117b4be6174b7b8533 (diff)
downloadlinux-8d21e9963bec1aad2280cdd034c8993033ef2948.tar.bz2
ip_gre: test csum_start instead of transport header
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@gmail.com/T/#u Fixes: 8a0ed250f911 ("ip_gre: validate csum_start only on pull") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com> Link: https://lore.kernel.org/r/20220606132107.3582565-1-willemdebruijn.kernel@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/ip_gre.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 7e474a85deaf..3b9cd487075a 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -629,21 +629,20 @@ 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;