[linux] 02/02: sctp: deny peeloff operation on asocs with threads sleeping on it (CVE-2017-6353)

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carnil pushed a commit to branch jessie-security
in repository linux.

commit 21d0ee3f0b88c88e36c5f0865810e6c023fbcb18
Author: Salvatore Bonaccorso <carnil at debian.org>
Date:   Tue Mar 7 17:24:28 2017 +0100

    sctp: deny peeloff operation on asocs with threads sleeping on it (CVE-2017-6353)
---
 debian/changelog                                   |  2 +
 ...eeloff-operation-on-asocs-with-threads-sl.patch | 66 ++++++++++++++++++++++
 debian/patches/series                              |  1 +
 3 files changed, 69 insertions(+)

diff --git a/debian/changelog b/debian/changelog
index d614514..6047115 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -2,6 +2,8 @@ linux (3.16.39-1+deb8u2) UNRELEASED; urgency=medium
 
   * ipc/shm: Fix shmat mmap nil-page protection (CVE-2017-5669)
   * sctp: avoid BUG_ON on sctp_wait_for_sndbuf (CVE-2017-5986)
+  * sctp: deny peeloff operation on asocs with threads sleeping on it
+    (CVE-2017-6353)
 
  -- Salvatore Bonaccorso <carnil at debian.org>  Tue, 07 Mar 2017 17:10:30 +0100
 
diff --git a/debian/patches/bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sl.patch b/debian/patches/bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sl.patch
new file mode 100644
index 0000000..5cd6632
--- /dev/null
+++ b/debian/patches/bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sl.patch
@@ -0,0 +1,66 @@
+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>
+---
+ net/sctp/socket.c | 8 ++++++--
+ 1 file changed, 6 insertions(+), 2 deletions(-)
+
+diff --git a/net/sctp/socket.c b/net/sctp/socket.c
+index b532148..465a9c8 100644
+--- a/net/sctp/socket.c
++++ b/net/sctp/socket.c
+@@ -4862,6 +4862,12 @@ int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id, struct socket **sockp)
+ 	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.
+ 	 */
+@@ -7599,8 +7605,6 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p,
+ 		 */
+ 		release_sock(sk);
+ 		current_timeo = schedule_timeout(current_timeo);
+-		if (sk != asoc->base.sk)
+-			goto do_error;
+ 		lock_sock(sk);
+ 
+ 		*timeo_p = current_timeo;
+-- 
+2.1.4
+
diff --git a/debian/patches/series b/debian/patches/series
index 735a523..50a0e35 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -695,6 +695,7 @@ bugfix/x86/kvm-fix-page-struct-leak-in-handle_vmon.patch
 bugfix/all/ipv4-keep-skb-dst-around-in-presence-of-ip-options.patch
 bugfix/all/ipc-shm-Fix-shmat-mmap-nil-page-protection.patch
 bugfix/all/sctp-avoid-BUG_ON-on-sctp_wait_for_sndbuf.patch
+bugfix/all/sctp-deny-peeloff-operation-on-asocs-with-threads-sl.patch
 
 # Fix ABI changes
 debian/of-fix-abi-changes.patch

-- 
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