packet: fix race condition in packet_set_ring (CVE-2016-8655)

debian/changelog

@@ -45,6 +45,7 @@ linux (4.8.12-1) UNRELEASED; urgency=medium
 
   [ Salvatore Bonaccorso ]
   * tipc: check minimum bearer MTU (CVE-2016-8632)
+  * packet: fix race condition in packet_set_ring (CVE-2016-8655)
 
  -- Uwe Kleine-König <ukleinek@debian.org>  Sun, 04 Dec 2016 21:16:06 +0100
 

debian/patches/bugfix/all/packet-fix-race-condition-in-packet_set_ring.patch

@@ -0,0 +1,92 @@
+From: Philip Pettersson <philip.pettersson@gmail.com>
+Date: Wed, 30 Nov 2016 14:55:36 -0800
+Subject: packet: fix race condition in packet_set_ring
+Origin: https://git.kernel.org/linus/84ac7260236a49c79eede91617700174c2c19b0c
+
+When packet_set_ring creates a ring buffer it will initialize a
+struct timer_list if the packet version is TPACKET_V3. This value
+can then be raced by a different thread calling setsockopt to
+set the version to TPACKET_V1 before packet_set_ring has finished.
+
+This leads to a use-after-free on a function pointer in the
+struct timer_list when the socket is closed as the previously
+initialized timer will not be deleted.
+
+The bug is fixed by taking lock_sock(sk) in packet_setsockopt when
+changing the packet version while also taking the lock at the start
+of packet_set_ring.
+
+Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
+Signed-off-by: Philip Pettersson <philip.pettersson@gmail.com>
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ net/packet/af_packet.c | 18 ++++++++++++------
+ 1 file changed, 12 insertions(+), 6 deletions(-)
+
+diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
+index d2238b2..dd23323 100644
+--- a/net/packet/af_packet.c
++++ b/net/packet/af_packet.c
+@@ -3648,19 +3648,25 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
+ 
+ 		if (optlen != sizeof(val))
+ 			return -EINVAL;
+-		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)
+-			return -EBUSY;
+ 		if (copy_from_user(&val, optval, sizeof(val)))
+ 			return -EFAULT;
+ 		switch (val) {
+ 		case TPACKET_V1:
+ 		case TPACKET_V2:
+ 		case TPACKET_V3:
+-			po->tp_version = val;
+-			return 0;
++			break;
+ 		default:
+ 			return -EINVAL;
+ 		}
++		lock_sock(sk);
++		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
++			ret = -EBUSY;
++		} else {
++			po->tp_version = val;
++			ret = 0;
++		}
++		release_sock(sk);
++		return ret;
+ 	}
+ 	case PACKET_RESERVE:
+ 	{
+@@ -4164,6 +4170,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
+ 	/* Added to avoid minimal code churn */
+ 	struct tpacket_req *req = &req_u->req;
+ 
++	lock_sock(sk);
+ 	/* Opening a Tx-ring is NOT supported in TPACKET_V3 */
+ 	if (!closing && tx_ring && (po->tp_version > TPACKET_V2)) {
+ 		net_warn_ratelimited("Tx-ring is not supported.\n");
+@@ -4245,7 +4252,6 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
+ 			goto out;
+ 	}
+ 
+-	lock_sock(sk);
+ 
+ 	/* Detach socket from network */
+ 	spin_lock(&po->bind_lock);
+@@ -4294,11 +4300,11 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
+ 		if (!tx_ring)
+ 			prb_shutdown_retire_blk_timer(po, rb_queue);
+ 	}
+-	release_sock(sk);
+ 
+ 	if (pg_vec)
+ 		free_pg_vec(pg_vec, order, req->tp_block_nr);
+ out:
++	release_sock(sk);
+ 	return err;
+ }
+ 
+-- 
+2.1.4
+

debian/patches/series

@@ -103,6 +103,7 @@ bugfix/all/fs-Avoid-premature-clearing-of-capabilities.patch
 bugfix/all/vfio-pci-Fix-integer-overflows-bitmask-check.patch
 bugfix/all/mnt-Add-a-per-mount-namespace-limit-on-the-number-of.patch
 bugfix/all/tipc-check-minimum-bearer-MTU.patch
+bugfix/all/packet-fix-race-condition-in-packet_set_ring.patch
 
 # ABI maintenance