linux-kernel - [ 012/135] net: sctp: fix smatch warning in sctp_send_asconf_del

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Message-Id: <20131011193946.576758122@linuxfoundation.org>
Date:	Fri, 11 Oct 2013 12:38:13 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
	Neil Horman <nhorman@...driver.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Michio Honda <micchie@....wide.ad.jp>,
	Vlad Yasevich <vyasevich@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 012/135] net: sctp: fix smatch warning in sctp_send_asconf_del_ip

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <dborkman@...hat.com>

[ Upstream commit 88362ad8f9a6cea787420b57cc27ccacef000dbe ]

This was originally reported in [1] and posted by Neil Horman [2], he said:

  Fix up a missed null pointer check in the asconf code. If we don't find
  a local address, but we pass in an address length of more than 1, we may
  dereference a NULL laddr pointer. Currently this can't happen, as the only
  users of the function pass in the value 1 as the addrcnt parameter, but
  its not hot path, and it doesn't hurt to check for NULL should that ever
  be the case.

The callpath from sctp_asconf_mgmt() looks okay. But this could be triggered
from sctp_setsockopt_bindx() call with SCTP_BINDX_REM_ADDR and addrcnt > 1
while passing all possible addresses from the bind list to SCTP_BINDX_REM_ADDR
so that we do *not* find a single address in the association's bind address
list that is not in the packed array of addresses. If this happens when we
have an established association with ASCONF-capable peers, then we could get
a NULL pointer dereference as we only check for laddr == NULL && addrcnt == 1
and call later sctp_make_asconf_update_ip() with NULL laddr.

BUT: this actually won't happen as sctp_bindx_rem() will catch such a case
and return with an error earlier. As this is incredably unintuitive and error
prone, add a check to catch at least future bugs here. As Neil says, its not
hot path. Introduced by 8a07eb0a5 ("sctp: Add ASCONF operation on the
single-homed host").

 [1] http://www.spinics.net/lists/linux-sctp/msg02132.html
 [2] http://www.spinics.net/lists/linux-sctp/msg02133.html

Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Neil Horman <nhorman@...driver.com>
Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
Cc: Michio Honda <micchie@....wide.ad.jp>
Acked-By: Neil Horman <nhorman@...driver.com>
Acked-by: Vlad Yasevich <vyasevich@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sctp/socket.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -812,6 +812,9 @@ static int sctp_send_asconf_del_ip(struc
 			goto skip_mkasconf;
 		}

+		if (laddr == NULL)
+			return -EINVAL;
+
 		/* We do not need RCU protection throughout this loop
 		 * because this is done under a socket lock from the
 		 * setsockopt call.

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