From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Eric Dumazet <edumazet@google.com>,
"David S. Miller" <davem@davemloft.net>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
Yuchung Cheng <ycheng@google.com>,
Jonathan Rajotte-Julien <joraj@efficios.com>
Subject: [regression] TC_MD5SIG on established sockets
Date: Wed, 13 May 2020 15:38:35 -0400 (EDT) [thread overview]
Message-ID: <341326348.19635.1589398715534.JavaMail.zimbra@efficios.com> (raw)
Hi,
I am reporting a regression with respect to use of TCP_MD5SIG/TCP_MD5SIG_EXT
on established sockets. It is observed by a customer.
This issue is introduced by this commit:
commit 721230326891 "tcp: md5: reject TCP_MD5SIG or TCP_MD5SIG_EXT on established sockets"
The intent of this commit appears to be to fix a use of uninitialized value in
tcp_parse_options(). The change introduced by this commit is to disallow setting
the TCP_MD5SIG{,_EXT} socket options on an established socket.
The justification for this change appears in the commit message:
"I believe this was caused by a TCP_MD5SIG being set on live
flow.
This is highly unexpected, since TCP option space is limited.
For instance, presence of TCP MD5 option automatically disables
TCP TimeStamp option at SYN/SYNACK time, which we can not do
once flow has been established.
Really, adding/deleting an MD5 key only makes sense on sockets
in CLOSE or LISTEN state."
However, reading through RFC2385 [1], this justification does not appear
correct. Quoting to the RFC:
"This password never appears in the connection stream, and the actual
form of the password is up to the application. It could even change
during the lifetime of a particular connection so long as this change
was synchronized on both ends"
The paragraph above clearly underlines that changing the MD5 signature of
a live TCP socket is allowed.
I also do not understand why it would be invalid to transition an established
TCP socket from no-MD5 to MD5, or transition from MD5 to no-MD5. Quoting the
RFC:
"The total header size is also an issue. The TCP header specifies
where segment data starts with a 4-bit field which gives the total
size of the header (including options) in 32-byte words. This means
that the total size of the header plus option must be less than or
equal to 60 bytes -- this leaves 40 bytes for options."
The paragraph above seems to be the only indication that some TCP options
cannot be combined on a given TCP socket: if the resulting header size does
not fit. However, I do not see anything in the specification preventing any
of the following use-cases on an established TCP socket:
- Transition from no-MD5 to MD5,
- Transition from MD5 to no-MD5,
- Changing the MD5 key associated with a socket.
As long as the resulting combination of options does not exceed the available
header space.
Can we please fix this KASAN report in a way that does not break user-space
applications expectations about Linux' implementation of RFC2385 ?
Thanks,
Mathieu
[1] RFC2385: https://tools.ietf.org/html/rfc2385
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next reply other threads:[~2020-05-13 19:38 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 19:38 Mathieu Desnoyers [this message]
2020-05-13 19:49 ` [regression] TC_MD5SIG on established sockets Eric Dumazet
2020-05-13 19:56 ` Eric Dumazet
2020-06-29 19:43 ` [regression] TCP_MD5SIG " Mathieu Desnoyers
2020-06-29 20:47 ` Eric Dumazet
2020-06-30 19:43 ` Linus Torvalds
2020-06-30 19:52 ` Linus Torvalds
2020-06-30 20:34 ` Mathieu Desnoyers
2020-06-30 20:39 ` Eric Dumazet
2020-06-30 20:44 ` David Miller
2020-06-30 20:56 ` Eric Dumazet
2020-06-30 21:17 ` Mathieu Desnoyers
2020-06-30 21:23 ` Eric Dumazet
2020-06-30 21:54 ` Eric Dumazet
2020-06-30 22:07 ` Eric Dumazet
2020-06-30 22:38 ` Eric Dumazet
2020-06-30 23:44 ` Mathieu Desnoyers
2020-07-01 0:01 ` Eric Dumazet
2020-07-01 2:02 ` Herbert Xu
2020-07-01 2:17 ` Eric Dumazet
2020-07-01 2:22 ` Herbert Xu
2020-07-01 2:30 ` Eric Dumazet
2020-07-01 2:39 ` Joe Perches
2020-07-01 2:58 ` Herbert Xu
2020-07-01 3:36 ` Eric Dumazet
2020-07-01 3:50 ` Herbert Xu
2020-07-01 12:19 ` Mathieu Desnoyers
2020-07-01 15:15 ` Eric Dumazet
2020-07-01 17:24 ` Eric Dumazet
2020-06-30 20:21 ` David Miller
2020-06-30 20:30 ` Eric Dumazet
2020-06-30 20:39 ` Mathieu Desnoyers
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