linux-kernel - [PATCH 3.2 54/61] sctp: do not peel off an assoc from one netns to another one

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Message-ID: <lsq.1511316666.834102421@decadent.org.uk>
Date:   Wed, 22 Nov 2017 02:11:06 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "ChunYu Wang" <chunwang@...hat.com>,
        "Neil Horman" <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Xin Long" <lucien.xin@...il.com>,
        "Marcelo Ricardo Leitner" <marcelo.leitner@...il.com>
Subject: [PATCH 3.2 54/61] sctp: do not peel off an assoc from one netns
 to another one

3.2.96-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Xin Long <lucien.xin@...il.com>

commit df80cd9b28b9ebaa284a41df611dbf3a2d05ca74 upstream.

Now when peeling off an association to the sock in another netns, all
transports in this assoc are not to be rehashed and keep use the old
key in hashtable.

As a transport uses sk->net as the hash key to insert into hashtable,
it would miss removing these transports from hashtable due to the new
netns when closing the sock and all transports are being freeed, then
later an use-after-free issue could be caused when looking up an asoc
and dereferencing those transports.

This is a very old issue since very beginning, ChunYu found it with
syzkaller fuzz testing with this series:

  socket$inet6_sctp()
  bind$inet6()
  sendto$inet6()
  unshare(0x40000000)
  getsockopt$inet_sctp6_SCTP_GET_ASSOC_ID_LIST()
  getsockopt$inet_sctp6_SCTP_SOCKOPT_PEELOFF()

This patch is to block this call when peeling one assoc off from one
netns to another one, so that the netns of all transport would not
go out-sync with the key in hashtable.

Note that this patch didn't fix it by rehashing transports, as it's
difficult to handle the situation when the tuple is already in use
in the new netns. Besides, no one would like to peel off one assoc
to another netns, considering ipaddrs, ifaces, etc. are usually
different.

Reported-by: ChunYu Wang <chunwang@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Acked-by: Neil Horman <nhorman@...driver.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2:
 - Add #include <linux/nsproxy.h>
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -71,6 +71,7 @@
 #include <linux/crypto.h>
 #include <linux/slab.h>
 #include <linux/compat.h>
+#include <linux/nsproxy.h>

 #include <net/ip.h>
 #include <net/icmp.h>
@@ -4242,6 +4243,10 @@ SCTP_STATIC int sctp_do_peeloff(struct s
 	struct sctp_af *af;
 	int err = 0;

+	/* Do not peel off from one netns to another one. */
+	if (!net_eq(current->nsproxy->net_ns, sock_net(sk)))
+		return -EINVAL;
+
 	/* If there is a thread waiting on more sndbuf space for
 	 * sending on this asoc, it cannot be peeled.
 	 */