netdev - Re: [PATCH v2 net 2/6] tcp: Fix bind() regression for v4-mapped-v6 wildcard address.

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Message-ID: <CANn89i+3Fgo+wez0zS9sDPnP-F_9HerX7cEELrC=9c1wcoxvoA@mail.gmail.com>
Date: Tue, 12 Sep 2023 06:58:27 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, 
	Joanne Koong <joannelkoong@...il.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	Andrei Vagin <avagin@...gle.com>
Subject: Re: [PATCH v2 net 2/6] tcp: Fix bind() regression for v4-mapped-v6
 wildcard address.

On Mon, Sep 11, 2023 at 8:38 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> Andrei Vagin reported bind() regression with strace logs.
>
> If we bind() a TCPv6 socket to ::FFFF:0.0.0.0 and then bind() a TCPv4
> socket to 127.0.0.1, the 2nd bind() should fail but now succeeds.
>
>   from socket import *
>
>   s1 = socket(AF_INET6, SOCK_STREAM)
>   s1.bind(('::ffff:0.0.0.0', 0))
>
>   s2 = socket(AF_INET, SOCK_STREAM)
>   s2.bind(('127.0.0.1', s1.getsockname()[1]))
>
> During the 2nd bind(), if tb->family is AF_INET6 and sk->sk_family is
> AF_INET in inet_bind2_bucket_match_addr_any(), we still need to check
> if tb has the v4-mapped-v6 wildcard address.
>
> The example above does not work after commit 5456262d2baa ("net: Fix
> incorrect address comparison when searching for a bind2 bucket"), but
> the blamed change is not the commit.
>
> Before the commit, the leading zeros of ::FFFF:0.0.0.0 were treated
> as 0.0.0.0, and the sequence above worked by chance.  Technically, this
> case has been broken since bhash2 was introduced.
>
> Note that if we bind() two sockets to 127.0.0.1 and then ::FFFF:0.0.0.0,
> the 2nd bind() fails properly because we fall back to using bhash to
> detect conflicts for the v4-mapped-v6 address.
>
> Fixes: 28044fc1d495 ("net: Add a bhash2 table hashed by port and address")
> Reported-by: Andrei Vagin <avagin@...gle.com>
> Closes: https://lore.kernel.org/netdev/ZPuYBOFC8zsK6r9T@google.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>