GIT: unionfs2-2.6.27.y: vfs: add NOFOLLOW flag to umount(2)

[Erez Zadok]

commit 23b5e014564bb71eb05871af019912957263f158
Author: Miklos Szeredi <mszeredi at suse.cz>
Date:   Wed Feb 10 12:15:53 2010 +0100

    vfs: add NOFOLLOW flag to umount(2)
    
    commit db1f05bb85d7966b9176e293f3ceead1cb8b5d79 upstream.
    
    Add a new UMOUNT_NOFOLLOW flag to umount(2).  This is needed to prevent
    symlink attacks in unprivileged unmounts (fuse, samba, ncpfs).
    
    Additionally, return -EINVAL if an unknown flag is used (and specify
    an explicitly unused flag: UMOUNT_UNUSED).  This makes it possible for
    the caller to determine if a flag is supported or not.
    
    CC: Eugene Teo <eugene at redhat.com>
    CC: Michael Kerrisk <mtk.manpages at gmail.com>
    Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>
    Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

diff --git a/fs/namespace.c b/fs/namespace.c
index efe0251..2083810 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1132,8 +1132,15 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 {
 	struct path path;
 	int retval;
+	int lookup_flags = 0;
 
-	retval = user_path(name, &path);
+	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
+		return -EINVAL;
+
+	if (!(flags & UMOUNT_NOFOLLOW))
+		lookup_flags |= LOOKUP_FOLLOW;
+
+	retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
 	if (retval)
 		goto out;
 	retval = -EINVAL;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 909e13e..248465c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1061,6 +1061,8 @@ extern int send_sigurg(struct fown_struct *fown);
 #define MNT_FORCE	0x00000001	/* Attempt to forcibily umount */
 #define MNT_DETACH	0x00000002	/* Just detach from the tree */
 #define MNT_EXPIRE	0x00000004	/* Mark for expiry */
+#define UMOUNT_NOFOLLOW	0x00000008	/* Don't follow symlink on umount */
+#define UMOUNT_UNUSED	0x80000000	/* Flag guaranteed to be unused */
 
 extern struct list_head super_blocks;
 extern spinlock_t sb_lock;