5.4-stable review patch. If anyone has any objections, please let me know.
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From: Anton Danilov littlesmilingcloud@gmail.com
[ Upstream commit c4a14f6d9d17ad1e41a36182dd3b8a5fd91efbd7 ]
Regression Description:
Depending on the options specified for the GRE tunnel device, small packets may be dropped. This occurs because the pskb_network_may_pull function fails due to the packet's insufficient length.
For example, if only the okey option is specified for the tunnel device, original (before encapsulation) packets smaller than 28 bytes (including the IPv4 header) will be dropped. This happens because the required length is calculated relative to the network header, not the skb->head.
Here is how the required length is computed and checked:
* The pull_len variable is set to 28 bytes, consisting of: * IPv4 header: 20 bytes * GRE header with Key field: 8 bytes
* The pskb_network_may_pull function adds the network offset, shifting the checkable space further to the beginning of the network header and extending it to the beginning of the packet. As a result, the end of the checkable space occurs beyond the actual end of the packet.
Instead of ensuring that 28 bytes are present in skb->head, the function is requesting these 28 bytes starting from the network header. For small packets, this requested length exceeds the actual packet size, causing the check to fail and the packets to be dropped.
This issue affects both locally originated and forwarded packets in DMVPN-like setups.
How to reproduce (for local originated packets):
ip link add dev gre1 type gre ikey 1.9.8.4 okey 1.9.8.4 \ local <your-ip> remote 0.0.0.0
ip link set mtu 1400 dev gre1 ip link set up dev gre1 ip address add 192.168.13.1/24 dev gre1 ip neighbor add 192.168.13.2 lladdr <remote-ip> dev gre1 ping -s 1374 -c 10 192.168.13.2 tcpdump -vni gre1 tcpdump -vni <your-ext-iface> 'ip proto 47' ip -s -s -d link show dev gre1
Solution:
Use the pskb_may_pull function instead the pskb_network_may_pull.
Fixes: 80d875cfc9d3 ("ipv4: ip_gre: Avoid skb_pull() failure in ipgre_xmit()") Signed-off-by: Anton Danilov littlesmilingcloud@gmail.com Reviewed-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20240924235158.106062-1-littlesmilingcloud@gmail.co... Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/ip_gre.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index 3aae46b845775..09e9e46259f70 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -635,11 +635,11 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb, if (skb_cow_head(skb, 0)) goto free_skb;
- tnl_params = (const struct iphdr *)skb->data; - - if (!pskb_network_may_pull(skb, pull_len)) + if (!pskb_may_pull(skb, pull_len)) goto free_skb;
+ tnl_params = (const struct iphdr *)skb->data; + /* ip_tunnel_xmit() needs skb->data pointing to gre header. */ skb_pull(skb, pull_len); skb_reset_mac_header(skb);