Re: [PATCH] [v2 netfilter-next] netfilter: nf_tables: fib warnings

Arnd Bergmann [off-list ref] wrote:

The newly added nft fib code produces two warnings:

net/ipv4/netfilter/nft_fib_ipv4.c: In function 'nft_fib4_eval':
net/ipv4/netfilter/nft_fib_ipv4.c:80:6: error: unused variable 'i' [-Werror=unused-variable]
net/ipv4/netfilter/nft_fib_ipv4.c: In function ‘nft_fib4_eval’:
net/ipv4/netfilter/nft_fib_ipv4.c:137:6: error: ‘oif’ may be used uninitialized in this function [-Werror=maybe-uninitialized]

The first one is obvious as the only user of that variable is
inside of an #ifdef

The second one is a bit trickier. It's clear that oif is in fact
uninitialized when it gets used when neither NFTA_FIB_F_IIF nor
NFTA_FIB_F_OIF are set, and just setting it to NULL won't work
as it may later get dereferenced.

However, there is no need to search the result list if it is
NULL, as Florian pointed out. This integrates his (untested)
change to do so. I have confirmed that the combined patch
solves both warnings, but as I don't fully understand Florian's
change, I can't tell if it's correct.

Suggested-by: Florian Westphal <fw@strlen.de>
Fixes: 84f5eedb983e ("netfilter: nf_tables: add fib expression")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

chain pre {
        type filter hook prerouting priority 0; policy accept;
        fib saddr oif "eth0"
}

eth0: default route, 192.168.7.10/16
eth1: 10.0.0.2/8

ping from 192.168.7.1 from peer on eth0: result eth0, ok
ping from 10.0.0.2 from peer on eth0: no result, ok
ping from 10.0.0.3 from peer on eth0: result eth1, ok

chain pre {
	        type filter hook prerouting priority 0; policy accept;
	        fib saddr . iif oif "eth0"
}

ping from 192.168.7.1 from peer on eth0: result eth0, ok
ping from 10.0.0.2 from peer on eth0: no result, ok
ping from 10.0.0.3 from peer on eth0: no result, ok

so:

Tested-by: Florian Westphal <fw@strlen.de>