[PATCH 4.1 043/159] CIFS: fix type confusion in copy offload ioctl

Greg Kroah-Hartman
2015-09-26T21:17:35Z

From: Jann Horn <jann@thejh.net>

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@thejh.net>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/cifs/ioctl.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/fs/cifs/ioctl.c
+++ b/fs/cifs/ioctl.c
@@ -67,6 +67,12 @@ static long cifs_ioctl_clone(unsigned in
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");