netdev - Re: [PATCH net 1/2] ipv4: Fix incorrect TOS in route get reply

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Message-ID: <91e2fa95-1db1-47a0-947a-82d7fcd762fe@kernel.org>
Date: Mon, 15 Jul 2024 15:33:29 -0700
From: David Ahern <dsahern@...nel.org>
To: Ido Schimmel <idosch@...dia.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 edumazet@...gle.com, gnault@...hat.com, roopa@...ulusnetworks.com
Subject: Re: [PATCH net 1/2] ipv4: Fix incorrect TOS in route get reply

On 7/15/24 7:23 AM, Ido Schimmel wrote:
> The TOS value that is returned to user space in the route get reply is
> the one with which the lookup was performed ('fl4->flowi4_tos'). This is
> fine when the matched route is configured with a TOS as it would not
> match if its TOS value did not match the one with which the lookup was
> performed.
> 
> However, matching on TOS is only performed when the route's TOS is not
> zero. It is therefore possible to have the kernel incorrectly return a
> non-zero TOS:
> 
>  # ip link add name dummy1 up type dummy
>  # ip address add 192.0.2.1/24 dev dummy1
>  # ip route get 192.0.2.2 tos 0xfc
>  192.0.2.2 tos 0x1c dev dummy1 src 192.0.2.1 uid 0
>      cache
> 
> Fix by adding a DSCP field to the FIB result structure (inside an
> existing 4 bytes hole), populating it in the route lookup and using it
> when filling the route get reply.
> 
> Output after the patch:
> 
>  # ip link add name dummy1 up type dummy
>  # ip address add 192.0.2.1/24 dev dummy1
>  # ip route get 192.0.2.2 tos 0xfc
>  192.0.2.2 dev dummy1 src 192.0.2.1 uid 0
>      cache
> 
> Fixes: 1a00fee4ffb2 ("ipv4: Remove rt_key_{src,dst,tos} from struct rtable.")
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> ---
>  include/net/ip_fib.h |  1 +
>  net/ipv4/fib_trie.c  |  1 +
>  net/ipv4/route.c     | 14 +++++++-------
>  3 files changed, 9 insertions(+), 7 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@...nel.org>