[3.16.y-ckt stable] Patch "CIFS: fix type confusion in copy offload ioctl" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    CIFS: fix type confusion in copy offload ioctl

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.19.8-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d575294a7b1ff93d6c92a9e9aad3af47d0a779e4 Mon Sep 17 00:00:00 2001
From: Jann Horn <jann at thejh.net>
Date: Fri, 11 Sep 2015 16:27:27 +0200
Subject: CIFS: fix type confusion in copy offload ioctl

commit 4c17a6d56bb0cad3066a714e94f7185a24b40f49 upstream.

This might lead to local privilege escalation (code execution as
kernel) for systems where the following conditions are met:

 - CONFIG_CIFS_SMB2 and CONFIG_CIFS_POSIX are enabled
 - a cifs filesystem is mounted where:
  - the mount option "vers" was used and set to a value >=2.0
  - the attacker has write access to at least one file on the filesystem

To attack this, an attacker would have to guess the target_tcon
pointer (but guessing wrong doesn't cause a crash, it just returns an
error code) and win a narrow race.

Signed-off-by: Jann Horn <jann at thejh.net>
Signed-off-by: Steve French <smfrench at gmail.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/cifs/ioctl.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/cifs/ioctl.c b/fs/cifs/ioctl.c
index 8b7898b..64a9bca 100644
--- a/fs/cifs/ioctl.c
+++ b/fs/cifs/ioctl.c
@@ -67,6 +67,12 @@ static long cifs_ioctl_clone(unsigned int xid, struct file *dst_file,
 		goto out_drop_write;
 	}

+	if (src_file.file->f_op->unlocked_ioctl != cifs_ioctl) {
+		rc = -EBADF;
+		cifs_dbg(VFS, "src file seems to be from a different filesystem type\n");
+		goto out_fput;
+	}
+
 	if ((!src_file.file->private_data) || (!dst_file->private_data)) {
 		rc = -EBADF;
 		cifs_dbg(VFS, "missing cifsFileInfo on copy range src file\n");
--
1.9.1