netdev - Re: [PATCH] inet: dont set inet_rcv

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Date:	Tue, 07 Sep 2010 23:52:02 +0200
From:	Krzysztof Olędzki <ole@....pl>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] inet: dont set inet_rcv_saddr in connect()

On 2010-09-07 23:35, Eric Dumazet wrote:
> Le mardi 07 septembre 2010 à 12:59 -0700, David Miller a écrit :
>
>> Eric, please just delete the code block instead of leaving it
>> there inside of an #if 0 block.
>>
>> If there is information conveyed by the unused code, add that
>> information to the nice comment you're adding :-)
>>
>
> Indeed ;)
>
> [PATCH] inet: dont set inet_rcv_saddr in connect()
>
> The following sequence :
>
> socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)
>
> connect(fd, {sa_family=AF_INET, sin_port=htons(xx),
> sin_addr=inet_addr("1.2.3.4")}, 28)
>
> 1) Does an implicit inet_autobind()
>    (using an INADDR_ANY address, and selecting a random port).
>
> 2) Does an ip4_datagram_connect() to specify the address/port of
> remote end point.
>
> Problem is ip4_datagram_connect() also sets inet->inet_rcv_saddr (from
> INADDR_ANY to IP source address, given the current route to remote end
> point). Only the first connect() on the socket does this. Following ones
> dont change the (possibly wrong) source address.
>
> This breaks the secondary UDP hash, based on (ADDRESS, port), that was
> computed by inet_autobind(). If more than 10 sockets are linked in
> primary hash chain, we can drop incoming packets because searches are
> done in wrong secondary hash chain.
>
> This also potentially breaks multiple connect() to change remote
> endpoints, because old source address might be non usable for packets to
> new destination.
>
> If route happens to change, then we should automatically change our
> source address too, at next sendmsg() call, and UDP code deals with this
> just fine.
>
> If an application needs to specify a precise source address, it must use
> bind() system call. connect() man page only refers to remote address,
> not local one.
>
> Reported-by: Krzysztof Olędzki <ole@....pl>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Tested-by: Krzysztof Piotr Oledzki <ole@....pl>

Best regards,

			Krzysztof Olędzki
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