kernel: add fix for CVE-2016-7117

This probably doesn't affect Gluon as nothing is using recvmmsg, but it's still a good idea to get this fixed ASAP.

kernel: add fix for CVE-2016-7117
9934d254 · Matthias Schiffer · e1808451 · 9934d254
Unverified Commit 9934d254 authored 8 years ago by Matthias Schiffer
--- a/patches/openwrt/0076-kernel-add-fix-for-CVE-2016-7117.patch
+++ b/patches/openwrt/0076-kernel-add-fix-for-CVE-2016-7117.patch
+From: Matthias Schiffer <mschiffer@universe-factory.net>
+Date: Tue, 11 Oct 2016 00:46:56 +0200
+Subject: kernel: add fix for CVE-2016-7117
+
+diff --git a/target/linux/generic/patches-3.18/010-net-Fix-use-after-free-in-the-recvmmsg-exit-path.patch b/target/linux/generic/patches-3.18/010-net-Fix-use-after-free-in-the-recvmmsg-exit-path.patch
+new file mode 100644
+index 0000000..98da375
+--- /dev/null
+++ b/target/linux/generic/patches-3.18/010-net-Fix-use-after-free-in-the-recvmmsg-exit-path.patch
+@@ -0,0 +1,95 @@
+From cdd1fd36f4b67d9fdbeb1a4d16025192d44a3e8b Mon Sep 17 00:00:00 2001
+Message-Id: <cdd1fd36f4b67d9fdbeb1a4d16025192d44a3e8b.1476139573.git.mschiffer@universe-factory.net>
+From: Arnaldo Carvalho de Melo <acme@redhat.com>
+Date: Mon, 14 Mar 2016 09:56:35 -0300
+Subject: [PATCH] net: Fix use after free in the recvmmsg exit path
+
+[ Upstream commit 34b88a68f26a75e4fded796f1a49c40f82234b7d ]
+
+The syzkaller fuzzer hit the following use-after-free:
+
+  Call Trace:
+   [<ffffffff8175ea0e>] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:295
+   [<ffffffff851cc31a>] __sys_recvmmsg+0x6fa/0x7f0 net/socket.c:2261
+   [<     inline     >] SYSC_recvmmsg net/socket.c:2281
+   [<ffffffff851cc57f>] SyS_recvmmsg+0x16f/0x180 net/socket.c:2270
+   [<ffffffff86332bb6>] entry_SYSCALL_64_fastpath+0x16/0x7a
+  arch/x86/entry/entry_64.S:185
+
+And, as Dmitry rightly assessed, that is because we can drop the
+reference and then touch it when the underlying recvmsg calls return
+some packets and then hit an error, which will make recvmmsg to set
+sock->sk->sk_err, oops, fix it.
+
+Reported-and-Tested-by: Dmitry Vyukov <dvyukov@google.com>
+Cc: Alexander Potapenko <glider@google.com>
+Cc: Eric Dumazet <edumazet@google.com>
+Cc: Kostya Serebryany <kcc@google.com>
+Cc: Sasha Levin <sasha.levin@oracle.com>
+Fixes: a2e2725541fa ("net: Introduce recvmmsg socket syscall")
+http://lkml.kernel.org/r/20160122211644.GC2470@redhat.com
+Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
+---
+ net/socket.c | 38 +++++++++++++++++++-------------------
+ 1 file changed, 19 insertions(+), 19 deletions(-)
+
+diff --git a/net/socket.c b/net/socket.c
+index 02fc7c8..7f61789 100644
+--- a/net/socket.c
++++ b/net/socket.c
+@@ -2410,31 +2410,31 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
+ 			break;
+ 	}
+ 
+-out_put:
+-	fput_light(sock->file, fput_needed);
+-
+ 	if (err == 0)
+-		return datagrams;
++		goto out_put;
+ 
+-	if (datagrams != 0) {
++	if (datagrams == 0) {
++		datagrams = err;
++		goto out_put;
++	}
++
++	/*
++	 * We may return less entries than requested (vlen) if the
++	 * sock is non block and there aren't enough datagrams...
++	 */
++	if (err != -EAGAIN) {
+ 		/*
+-		 * We may return less entries than requested (vlen) if the
+-		 * sock is non block and there aren't enough datagrams...
++		 * ... or  if recvmsg returns an error after we
++		 * received some datagrams, where we record the
++		 * error to return on the next call or if the
++		 * app asks about it using getsockopt(SO_ERROR).
+ 		 */
+-		if (err != -EAGAIN) {
+-			/*
+-			 * ... or  if recvmsg returns an error after we
+-			 * received some datagrams, where we record the
+-			 * error to return on the next call or if the
+-			 * app asks about it using getsockopt(SO_ERROR).
+-			 */
+-			sock->sk->sk_err = -err;
+-		}
+-
+-		return datagrams;
++		sock->sk->sk_err = -err;
+ 	}
++out_put:
++	fput_light(sock->file, fput_needed);
+ 
+-	return err;
++	return datagrams;
+ }
+ 
+ SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg,
+-- 
+2.10.0
+