[PATCH] vfs: define new lookup flag for chdir

In the "operation does permission checking" model used by fuse, chdir
permission is not checked, since there's no chdir method.

For this case set a lookup flag, which will be passed to ->permission(), so
fuse can distinguish it from permission checks for other operations.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/fuse/dir.c

@@ -776,7 +776,7 @@ static int fuse_permission(struct inode *inode, int mask, struct nameidata *nd)
 		if ((mask & MAY_EXEC) && !S_ISDIR(mode) && !(mode & S_IXUGO))
 			return -EACCES;
 
-		if (nd && (nd->flags & LOOKUP_ACCESS))
+		if (nd && (nd->flags & (LOOKUP_ACCESS | LOOKUP_CHDIR)))
 			return fuse_access(inode, mask);
 		return 0;
 	}

fs/open.c

@@ -546,7 +546,8 @@ asmlinkage long sys_chdir(const char __user * filename)
 	struct nameidata nd;
 	int error;
 
-	error = __user_walk(filename, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &nd);
+	error = __user_walk(filename,
+			    LOOKUP_FOLLOW|LOOKUP_DIRECTORY|LOOKUP_CHDIR, &nd);
 	if (error)
 		goto out;
 

include/linux/namei.h

@@ -54,6 +54,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
 #define LOOKUP_OPEN		(0x0100)
 #define LOOKUP_CREATE		(0x0200)
 #define LOOKUP_ACCESS		(0x0400)
+#define LOOKUP_CHDIR		(0x0800)
 
 extern int FASTCALL(__user_walk(const char __user *, unsigned, struct nameidata *));
 extern int FASTCALL(__user_walk_fd(int dfd, const char __user *, unsigned, struct nameidata *));