Subject: Re: [PATCH net] ipv4: initialize flowi4_flags before calling fib_lookup()

From: David Ahern <[email-masked]>
Date: Tue, 22 Mar 2016 12:29:02 -0600

On 3/22/16 9:31 AM, 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 fl4.flowi4_flags to zero.
>
> Signed-off-by: Lance Richardson <[email-masked]>
> ---
>   net/ipv4/fib_frontend.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 21add55..896844a 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -304,6 +304,7 @@ __be32 fib_compute_spec_dst(struct sk_buff *skb)
>   		fl4.flowi4_scope = scope;
>   		fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;
>   		fl4.flowi4_tun_key.tun_id = 0;
> +		fl4.flowi4_flags = 0;
>   		if (!fib_lookup(net, &fl4, &res, 0))
>   			return FIB_RES_PREFSRC(net, res);
>   	} else {
>

Fixes: 58189ca7b2741 ("net: Fix vti use case with oif in dst lookups")

I think a more robust solution is to move fl4 to this if case and init 
when it is declared:

	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,
	};