[PATCH 4.7 026/184] kcm: fix a socket double free

[Greg Kroah-Hartman]

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: WANG Cong <xiyou.wangcong@xxxxxxxxx>


[ Upstream commit c0338aff2260ea6c092806312dbb154cec07a242 ]

Dmitry reported a double free on kcm socket, which could
be easily reproduced by:

	#include <unistd.h>
	#include <sys/syscall.h>

	int main()
	{
	  int fd = syscall(SYS_socket, 0x29ul, 0x5ul, 0x0ul, 0, 0, 0);
	  syscall(SYS_ioctl, fd, 0x89e2ul, 0x20a98000ul, 0, 0, 0);
	  return 0;
	}

This is because on the error path, after we install
the new socket file, we call sock_release() to clean
up the socket, which leaves the fd pointing to a freed
socket. Fix this by calling sys_close() on that fd
directly.

Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Tom Herbert <tom@xxxxxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/kcm/kcmsock.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -13,6 +13,7 @@
 #include <linux/socket.h>
 #include <linux/uaccess.h>
 #include <linux/workqueue.h>
+#include <linux/syscalls.h>
 #include <net/kcm.h>
 #include <net/netns/generic.h>
 #include <net/sock.h>
@@ -2035,7 +2036,7 @@ static int kcm_ioctl(struct socket *sock
 			if (copy_to_user((void __user *)arg, &info,
 					 sizeof(info))) {
 				err = -EFAULT;
-				sock_release(newsock);
+				sys_close(info.fd);
 			}
 		}