CVE-2016-8655

PKGBUILD

@@ -6,9 +6,9 @@ pkgbase=linux               # Build stock -ARCH kernel
 #pkgbase=linux-custom       # Build kernel with a different name
 _srcname=linux-4.8
 pkgver=4.8.12
-pkgrel=1
+pkgrel=2
 arch=('i686' 'x86_64')
-url="http://www.kernel.org/"
+url="https://www.kernel.org/"
 license=('GPL2')
 makedepends=('xmlto' 'docbook-xsl' 'kmod' 'inetutils' 'bc' 'libelf')
 options=('!strip')
@@ -23,6 +23,7 @@ source=("https://www.kernel.org/pub/linux/kernel/v4.x/${_srcname}.tar.xz"
         # standard config files for mkinitcpio ramdisk
         'linux.preset'
         'change-default-console-loglevel.patch'
+        fix_race_condition_in_packet_set_ring.diff
         )
 
 sha256sums=('3e9150065f193d3d94bcf46a1fe9f033c7ef7122ab71d75a7fb5a2f0c9a7e11a'
@@ -33,7 +34,8 @@ sha256sums=('3e9150065f193d3d94bcf46a1fe9f033c7ef7122ab71d75a7fb5a2f0c9a7e11a'
             '41b9a64542befd2fea170776e8ec22a7d158dd3273633afc9b91662c448cd90a'
             '834bd254b56ab71d73f59b3221f056c72f559553c04718e350ab2a3e2991afe0'
             'ad6344badc91ad0630caacde83f7f9b97276f80d26a20619a87952be65492c65'
-            '1256b241cd477b265a3c2d64bdc19ffe3c9bbcee82ea3994c590c2c76e767d99')
+            '1256b241cd477b265a3c2d64bdc19ffe3c9bbcee82ea3994c590c2c76e767d99'
+            'ad1ee95f906f88d31fcdb9273cd08e02e8eda177449f0c98dc1bff8cbf1483c2')
 validpgpkeys=(
               'ABAF11C65A2970B130ABE3C479BE3E4300411886' # Linus Torvalds
               '647F28654894E3BD457199BE38DBBDC86092693E' # Greg Kroah-Hartman
@@ -47,6 +49,10 @@ prepare() {
   # add upstream patch
   patch -p1 -i "${srcdir}/patch-${pkgver}"
 
+  # fix a race condition that allows to gain root
+  # https://marc.info/?l=linux-netdev&m=148054660230570&w=2
+  patch -p1 -i "${srcdir}/fix_race_condition_in_packet_set_ring.diff"
+
   # add latest fixes from stable queue, if needed
   # http://git.kernel.org/?p=linux/kernel/git/stable/stable-queue.git
 

fix_race_condition_in_packet_set_ring.diff

@@ -0,0 +1,84 @@
+From: Philip Pettersson <philip.pettersson@gmail.com>
+
+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>
+---
+ 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 d2238b204691b8e4f2e3acb9bc167b553ba32d50..dd2332390c45bbff7c3fc5d259453f2e1ca352bf 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;
+ }