[PATCH] net: ipv4: Remove MTU check in IP_HDRINCL send flow

[PATCH] net: ipv4: Remove MTU check in IP_HDRINCL send flow

[Yonatan Goldschmidt]

IP fragmentation can be performed as expected down the stack, without touching
irrelevant fields in the included header besides fragment offset, setting
IP_MF and header checksum.
If the included header has IP_DF set, EMSGSIZE is returned.

This allows users of IP_HDRINCL to have the kernel perform fragmentation.

Signed-off-by: Yonatan Goldschmidt <dev.jongy@gmail.com>
---
 net/ipv4/raw.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 125c1eab3eaa..63167abff05b 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -359,11 +359,6 @@ static int raw_send_hdrinc(struct sock *sk, struct
flowi*,
        struct rtable *rt = *rtp;
        int hlen, tlen;

-       if (length > rt->dst.dev->mtu) {
-               ip_local_error(sk, EMSGSIZE, fl4->daddr,
inet->inet_dport,
-                              rt->dst.dev->mtu);
-               return -EMSGSIZE;
-       }
        if (length < sizeof(struct iphdr))
                return -EINVAL;

Re: [PATCH] net: ipv4: Remove MTU check in IP_HDRINCL send flow

[David Miller]

From: Yonatan Goldschmidt <dev.jongy@gmail.com>
Date: Sun, 7 Jan 2018 01:26:48 +0200

> IP fragmentation can be performed as expected down the stack, without touching
> irrelevant fields in the included header besides fragment offset, setting
> IP_MF and header checksum.
> If the included header has IP_DF set, EMSGSIZE is returned.
> 
> This allows users of IP_HDRINCL to have the kernel perform fragmentation.
> 
> Signed-off-by: Yonatan Goldschmidt <dev.jongy@gmail.com>

This has been brought up before and we decided that for RAW sockets
the user is responsible for fragmentation, and the kernel should not
"manage" the packet given to it in any way whatsoever.