[linux] 07/07: sctp: deny peeloff operation on asocs with threads sleeping on it (CVE-2017-6353)

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benh pushed a commit to branch wheezy-security
in repository linux.

commit 68b23c198725ae28282cb7343bf2a3bc0954e82b
Author: Ben Hutchings <ben at decadent.org.uk>
Date:   Tue Mar 7 02:25:20 2017 +0000

    sctp: deny peeloff operation on asocs with threads sleeping on it (CVE-2017-6353)
---
 debian/changelog                                   |  2 +
 ...tion-on-asocs-with-threads-sleeping-on-it.patch | 63 ++++++++++++++++++++++
 debian/patches/series                              |  1 +
 3 files changed, 66 insertions(+)

diff --git a/debian/changelog b/debian/changelog
index 4c2a4ea..a08bf62 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -82,6 +82,8 @@ linux (3.2.86-1) UNRELEASED; urgency=medium
   * net/llc: avoid BUG_ON() in skb_orphan() (CVE-2017-6345)
   * packet: fix races in fanout_add() (CVE-2017-6346)
   * irda: Fix locking in hashbin_delete() (CVE-2017-6348)
+  * sctp: deny peeloff operation on asocs with threads sleeping on it
+    (CVE-2017-6353)
 
  -- Ben Hutchings <ben at decadent.org.uk>  Tue, 07 Mar 2017 01:47:48 +0000
 
diff --git a/debian/patches/bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sleeping-on-it.patch b/debian/patches/bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sleeping-on-it.patch
new file mode 100644
index 0000000..dcf9e37
--- /dev/null
+++ b/debian/patches/bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sleeping-on-it.patch
@@ -0,0 +1,63 @@
+From: Marcelo Ricardo Leitner <marcelo.leitner at gmail.com>
+Date: Thu, 23 Feb 2017 09:31:18 -0300
+Subject: sctp: deny peeloff operation on asocs with threads sleeping on it
+Origin: https://git.kernel.org/linus/dfcb9f4f99f1e9a49e43398a7bfbf56927544af1
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-6353
+
+commit 2dcab5984841 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf")
+attempted to avoid a BUG_ON call when the association being used for a
+sendmsg() is blocked waiting for more sndbuf and another thread did a
+peeloff operation on such asoc, moving it to another socket.
+
+As Ben Hutchings noticed, then in such case it would return without
+locking back the socket and would cause two unlocks in a row.
+
+Further analysis also revealed that it could allow a double free if the
+application managed to peeloff the asoc that is created during the
+sendmsg call, because then sctp_sendmsg() would try to free the asoc
+that was created only for that call.
+
+This patch takes another approach. It will deny the peeloff operation
+if there is a thread sleeping on the asoc, so this situation doesn't
+exist anymore. This avoids the issues described above and also honors
+the syscalls that are already being handled (it can be multiple sendmsg
+calls).
+
+Joint work with Xin Long.
+
+Fixes: 2dcab5984841 ("sctp: avoid BUG_ON on sctp_wait_for_sndbuf")
+Cc: Alexander Popov <alex.popov at linux.com>
+Cc: Ben Hutchings <ben at decadent.org.uk>
+Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner at gmail.com>
+Signed-off-by: Xin Long <lucien.xin at gmail.com>
+Signed-off-by: David S. Miller <davem at davemloft.net>
+[bwh: Backported to 3.2: adjust context]
+Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
+---
+ net/sctp/socket.c | 8 ++++++--
+ 1 file changed, 6 insertions(+), 2 deletions(-)
+
+--- a/net/sctp/socket.c
++++ b/net/sctp/socket.c
+@@ -4241,6 +4241,12 @@ int sctp_do_peeloff(struct sock *sk, sct
+ 	if (!asoc)
+ 		return -EINVAL;
+ 
++	/* If there is a thread waiting on more sndbuf space for
++	 * sending on this asoc, it cannot be peeled.
++	 */
++	if (waitqueue_active(&asoc->wait))
++		return -EBUSY;
++
+ 	/* An association cannot be branched off from an already peeled-off
+ 	 * socket, nor is this supported for tcp style sockets.
+ 	 */
+@@ -6480,8 +6486,6 @@ static int sctp_wait_for_sndbuf(struct s
+ 		 */
+ 		sctp_release_sock(sk);
+ 		current_timeo = schedule_timeout(current_timeo);
+-		if (sk != asoc->base.sk)
+-			goto do_error;
+ 		sctp_lock_sock(sk);
+ 
+ 		*timeo_p = current_timeo;
diff --git a/debian/patches/series b/debian/patches/series
index 4a9f973..8ebf251 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -1111,6 +1111,7 @@ bugfix/all/sctp-avoid-bug_on-on-sctp_wait_for_sndbuf.patch
 bugfix/all/net-llc-avoid-bug_on-in-skb_orphan.patch
 bugfix/all/packet-fix-races-in-fanout_add.patch
 bugfix/all/irda-fix-lockdep-annotations-in-hashbin_delete.patch
+bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sleeping-on-it.patch
 
 # ABI maintenance
 debian/perf-hide-abi-change-in-3.2.30.patch

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