netdev - Re: [PATCH net] ipv4: initialize flowi4_flags before calling fib

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Date:	Wed, 23 Mar 2016 14:35:38 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Lance Richardson <lrichard@...hat.com>, netdev@...r.kernel.org
Cc:	dsa@...ulusnetworks.com
Subject: Re: [PATCH net] ipv4: initialize flowi4_flags before calling
 fib_lookup()

Hello.

On 3/22/2016 9:56 PM, Lance Richardson wrote:

> Field fl4.flowi4_flags is not initialized in fib_compute_spec_dst()
> before calling fib_lookup(), which means fib_table_lookup() is
> using non-deterministic data at this line:
>
> 	if (!(flp->flowi4_flags & FLOWI_FLAG_SKIP_NH_OIF)) {
>
> Fix by initializing the entire fl4 structure, which will prevent
> similar issues as fields are added in the future by ensuring that
> all fields are initialized to zero unless explicitly initialized
> to another value.
>
> Fixes: 58189ca7b2741 ("net: Fix vti use case with oif in dst lookups")
> Suggested-by: David Ahern <dsa@...ulusnetworks.com>
> Signed-off-by: Lance Richardson <lrichard@...hat.com>
> ---
>   net/ipv4/fib_frontend.c | 16 +++++++---------
>   1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 21add55..8a9246d 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
[...]
> @@ -296,14 +295,13 @@ __be32 fib_compute_spec_dst(struct sk_buff *skb)
>
>   	scope = RT_SCOPE_UNIVERSE;
>   	if (!ipv4_is_zeronet(ip_hdr(skb)->saddr)) {
> -		fl4.flowi4_oif = 0;
> -		fl4.flowi4_iif = LOOPBACK_IFINDEX;
> -		fl4.daddr = ip_hdr(skb)->saddr;
> -		fl4.saddr = 0;
> -		fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
> -		fl4.flowi4_scope = scope;
> -		fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;
> -		fl4.flowi4_tun_key.tun_id = 0;
> +		struct flowi4 fl4 = {
> +			.flowi4_iif = LOOPBACK_IFINDEX,
> +			.daddr = ip_hdr(skb)->saddr,
> +			.flowi4_tos = RT_TOS(ip_hdr(skb)->tos),
> +			.flowi4_scope = scope,
> +			.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0,
> +		};

    Need empty line after the declaration.

>   		if (!fib_lookup(net, &fl4, &res, 0))
>   			return FIB_RES_PREFSRC(net, res);
>   	} else {

MBR, Sergei