linux-kernel - Re: [PATCH net] ipv4: ping: fix bind address validity check

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Message-Id: <CKSA92SUUX9U.33CY0D74VSKCS@enhorning>
Date:   Fri, 17 Jun 2022 10:56:56 +0200
From:   "Riccardo Paolo Bestetti" <pbl@...tov.io>
To:     "Carlos Llamas" <cmllamas@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        "Hideaki YOSHIFUJI" <yoshfuji@...ux-ipv6.org>,
        "David Ahern" <dsahern@...nel.org>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Jakub Kicinski" <kuba@...nel.org>,
        "Paolo Abeni" <pabeni@...hat.com>
Cc:     <kernel-team@...roid.com>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, "Miaohe Lin" <linmiaohe@...wei.com>,
        "Maciej Żenczykowski" <maze@...gle.com>
Subject: Re: [PATCH net] ipv4: ping: fix bind address validity check

On Fri Jun 17, 2022 at 4:02 AM CEST, Carlos Llamas wrote:
> Commit 8ff978b8b222 ("ipv4/raw: support binding to nonlocal addresses")
> introduced a helper function to fold duplicated validity checks of bind
> addresses into inet_addr_valid_or_nonlocal(). However, this caused an
> unintended regression in ping_check_bind_addr(), which previously would
> reject binding to multicast and broadcast addresses, but now these are
> both incorrectly allowed as reported in [1].
>
> This patch restores the original check. A simple reordering is done to
> improve readability and make it evident that multicast and broadcast
> addresses should not be allowed. Also, add an early exit for INADDR_ANY
> which replaces lost behavior added by commit 0ce779a9f501 ("net: Avoid
> unnecessary inet_addr_type() call when addr is INADDR_ANY").

Like I mentioned in one of my follow-ups to [1], I think a proper patch
for this not only restores the original behaviour, but also includes
regression tests (if we had it we wouldn't be needing this patch in the
first place; as one would expect, the regression escaped multiple human
reviews :)

I'm following up this email with a v2 to have that.

Riccardo P. Bestetti


>
> [1] https://lore.kernel.org/netdev/CANP3RGdkAcDyAZoT1h8Gtuu0saq+eOrrTiWbxnOs+5zn+cpyKg@mail.gmail.com/
>
> Fixes: 8ff978b8b222 ("ipv4/raw: support binding to nonlocal addresses")
> Cc: Miaohe Lin <linmiaohe@...wei.com>
> Cc: Riccardo Paolo Bestetti <pbl@...tov.io>
> Reported-by: Maciej Żenczykowski <maze@...gle.com>
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
> ---
>  net/ipv4/ping.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
> index 1a43ca73f94d..3c6101def7d6 100644
> --- a/net/ipv4/ping.c
> +++ b/net/ipv4/ping.c
> @@ -319,12 +319,16 @@ static int ping_check_bind_addr(struct sock *sk, struct inet_sock *isk,
>  		pr_debug("ping_check_bind_addr(sk=%p,addr=%pI4,port=%d)\n",
>  			 sk, &addr->sin_addr.s_addr, ntohs(addr->sin_port));
>  
> +		if (addr->sin_addr.s_addr == htonl(INADDR_ANY))
> +			return 0;
> +
>  		tb_id = l3mdev_fib_table_by_index(net, sk->sk_bound_dev_if) ? : tb_id;
>  		chk_addr_ret = inet_addr_type_table(net, addr->sin_addr.s_addr, tb_id);
>  
> -		if (!inet_addr_valid_or_nonlocal(net, inet_sk(sk),
> -					         addr->sin_addr.s_addr,
> -	                                         chk_addr_ret))
> +		if (chk_addr_ret == RTN_MULTICAST ||
> +		    chk_addr_ret == RTN_BROADCAST ||
> +		    (chk_addr_ret != RTN_LOCAL &&
> +		     !inet_can_nonlocal_bind(net, isk)))
>  			return -EADDRNOTAVAIL;
>  
>  #if IS_ENABLED(CONFIG_IPV6)
> -- 
> 2.36.1.476.g0c4daa206d-goog