netdev - Re: [PATCH net-next] net: metrics: add proper netlink validation

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Date:   Mon, 4 Jun 2018 16:54:03 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] net: metrics: add proper netlink validation

On 6/4/18 4:46 PM, Eric Dumazet wrote:
> Before using nla_get_u32(), better make sure the attribute
> is of the proper size.
> 
> Code recently was changed, but bug has been there from beginning
> of git.
> 
...
> 
> Fixes: a919525ad832 ("net: Move fib_convert_metrics to metrics file")

That commit just moved the code from 1 file to another. The previous
commit id is 6cf9dfd3bd62e, but it just moved code to a helper. The
originating commit id for the ip_metrics_convert bug is:

ea697639992d9 ("net: tcp: add RTAX_CC_ALGO fib handling")


> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Cc: David Ahern <dsahern@...il.com>
> ---
>  net/ipv4/fib_semantics.c | 2 ++
>  net/ipv4/metrics.c       | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> index 6608db23f54b6afdac0455650b47d64b1b22b255..9a890be8a0265edb78da225a82e2cac120f2150f 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -717,6 +717,8 @@ bool fib_metrics_match(struct fib_config *cfg, struct fib_info *fi)
>  			nla_strlcpy(tmp, nla, sizeof(tmp));
>  			val = tcp_ca_get_key_by_name(fi->fib_net, tmp, &ecn_ca);
>  		} else {
> +			if (nla_len(nla) != sizeof(u32)
> +				return false;
>  			val = nla_get_u32(nla);
>  		}
>  
> diff --git a/net/ipv4/metrics.c b/net/ipv4/metrics.c
> index 5121c6475e6b0e9a9a158d4cee473f52cd4d8efe..04311f7067e2e9e3dafb89aa4f8e30dab0fde854 100644
> --- a/net/ipv4/metrics.c
> +++ b/net/ipv4/metrics.c
> @@ -32,6 +32,8 @@ int ip_metrics_convert(struct net *net, struct nlattr *fc_mx, int fc_mx_len,
>  			if (val == TCP_CA_UNSPEC)
>  				return -EINVAL;
>  		} else {
> +			if (nla_len(nla) != sizeof(u32))
> +				return -EINVAL;
>  			val = nla_get_u32(nla);
>  		}
>  		if (type == RTAX_ADVMSS && val > 65535 - 40)
>