vfs: re-introduce MAY_CHDIR

Currently MAY_ACCESS means that filesystems must check the permissions
right then and not rely on cached results or the results of future
operations on the object.  This can be because of a call to sys_access() or
because of a call to chdir() which needs to check search without relying on
any future operations inside that dir.  I plan to use MAY_ACCESS for other
purposes in the security system, so I split the MAY_ACCESS and the
MAY_CHDIR cases.
Signed-off-by: NEric Paris <eparis@redhat.com>
Acked-by: NStephen D. Smalley <sds@tycho.nsa.gov>
Signed-off-by: NJames Morris <jmorris@namei.org>

fs/fuse/dir.c

@@ -1016,7 +1016,7 @@ static int fuse_permission(struct inode *inode, int mask)
 		   exist.  So if permissions are revoked this won't be
 		   noticed immediately, only after the attribute
 		   timeout has expired */
-	} else if (mask & MAY_ACCESS) {
+	} else if (mask & (MAY_ACCESS | MAY_CHDIR)) {
 		err = fuse_access(inode, mask);
 	} else if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode)) {
 		if (!(inode->i_mode & S_IXUGO)) {

fs/nfs/dir.c

@@ -1953,7 +1953,7 @@ int nfs_permission(struct inode *inode, int mask)
 	if ((mask & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
 		goto out;
 	/* Is this sys_access() ? */
-	if (mask & MAY_ACCESS)
+	if (mask & (MAY_ACCESS | MAY_CHDIR))
 		goto force_lookup;
 
 	switch (inode->i_mode & S_IFMT) {

fs/open.c

@@ -366,7 +366,7 @@ SYSCALL_DEFINE1(chdir, const char __user *, filename)
 	if (error)
 		goto out;
 
-	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_ACCESS);
+	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
 	if (error)
 		goto dput_and_out;
 
@@ -395,7 +395,7 @@ SYSCALL_DEFINE1(fchdir, unsigned int, fd)
 	if (!S_ISDIR(inode->i_mode))
 		goto out_putf;
 
-	error = inode_permission(inode, MAY_EXEC | MAY_ACCESS);
+	error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
 	if (!error)
 		set_fs_pwd(current->fs, &file->f_path);
 out_putf:
@@ -413,7 +413,7 @@ SYSCALL_DEFINE1(chroot, const char __user *, filename)
 	if (error)
 		goto out;
 
-	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_ACCESS);
+	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
 	if (error)
 		goto dput_and_out;
 

include/linux/fs.h

@@ -53,6 +53,7 @@ struct inodes_stat_t {
 #define MAY_APPEND 8
 #define MAY_ACCESS 16
 #define MAY_OPEN 32
+#define MAY_CHDIR 64
 
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond