[PATCH net-next v2] ipv6: discard fragment queue earlier if there is malformed datagram

Currently the kernel IPv6 implementation is not dicarding the fragment
queue upon receiving a IPv6 fragment that is not 8 bytes aligned. It
relies on queue expiration to free the queue.

While RFC 8200 section 4.5 does not explicitly mention that the rest of
fragments must be discarded, it does not make sense to keep them. The
parameter problem message is sent regardless that. In addition, if the
sender is able to re-compose the datagram so it is 8 bytes aligned it
would qualify as a new whole datagram not fitting into the same fragment
queue.

The same situation happens if segment end is exceeding the IPv6 maximum
packet length. The sooner we can free resources the better during
reassembly, the better.

Signed-off-by: Fernando Fernandez Mancera <redacted>
---
v2: handle segment end bigger than IPv6 maximum packet length 
---
 net/ipv6/reassembly.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 25ec8001898d..11f9144bebbe 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c

@@ -132,6 +132,9 @@ static int ip6_frag_queue(struct net *net,
 		/* note that if prob_offset is set, the skb is freed elsewhere,
 		 * we do not free it here.
 		 */
+		inet_frag_kill(&fq->q, refs);
+		__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
+				IPSTATS_MIB_REASMFAILS);
 		return -1;
 	}
 

@@ -163,6 +166,9 @@ static int ip6_frag_queue(struct net *net,
 			 * this case. -DaveM
 			 */
 			*prob_offset = offsetof(struct ipv6hdr, payload_len);
+			inet_frag_kill(&fq->q, refs);
+			__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
+					IPSTATS_MIB_REASMFAILS);
 			return -1;
 		}
 		if (end > fq->q.len) {

-- 
2.53.0

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski [off-list ref]:

On Wed, 25 Feb 2026 14:37:58 +0100 you wrote:

Currently the kernel IPv6 implementation is not dicarding the fragment
queue upon receiving a IPv6 fragment that is not 8 bytes aligned. It
relies on queue expiration to free the queue.

While RFC 8200 section 4.5 does not explicitly mention that the rest of
fragments must be discarded, it does not make sense to keep them. The
parameter problem message is sent regardless that. In addition, if the
sender is able to re-compose the datagram so it is 8 bytes aligned it
would qualify as a new whole datagram not fitting into the same fragment
queue.

[...]

Here is the summary with links:
  - [net-next,v2] ipv6: discard fragment queue earlier if there is malformed datagram
    https://git.kernel.org/netdev/net-next/c/9ff2d2a98370

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

On Sat, Feb 28, 2026 at 4:20 AM [off-list ref] wrote:

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski [off-list ref]:

On Wed, 25 Feb 2026 14:37:58 +0100 you wrote:

quoted

Currently the kernel IPv6 implementation is not dicarding the fragment
queue upon receiving a IPv6 fragment that is not 8 bytes aligned. It
relies on queue expiration to free the queue.

While RFC 8200 section 4.5 does not explicitly mention that the rest of
fragments must be discarded, it does not make sense to keep them. The
parameter problem message is sent regardless that. In addition, if the
sender is able to re-compose the datagram so it is 8 bytes aligned it
would qualify as a new whole datagram not fitting into the same fragment
queue.

[...]

Here is the summary with links:
  - [net-next,v2] ipv6: discard fragment queue earlier if there is malformed datagram
    https://git.kernel.org/netdev/net-next/c/9ff2d2a98370

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

I somehow missed the V2

Reviewed-by: Eric Dumazet <edumazet@google.com>

Thanks.