[PATCH] move executable checking into ->permission()

For execute permission on a regular files we need to check if file has
any execute bits at all, regardless of capabilites.

This check is normally performed by generic_permission() but was also
added to the case when the filesystem defines its own ->permission()
method. In the latter case the filesystem should be responsible for
performing this check.

Move the check from inode_permission() inside filesystems which are
not calling generic_permission().

Create a helper function execute_ok() that returns true if the inode
is a directory or if any execute bits are present in i_mode.

Also fix up the following code:

- coda control file is never executable
- sysctl files are never executable
- hfs_permission seems broken on MAY_EXEC, remove
- hfsplus_permission is eqivalent to generic_permission(), remove

Signed-off-by: Miklos Szeredi <[e-mail]>

fs/cifs/cifsfs.c

···
 
 	cifs_sb = CIFS_SB(inode->i_sb);
 
-	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_PERM)
-		return 0;
-	else /* file mode might have been restricted at mount time
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_PERM) {
+		if ((mask & MAY_EXEC) && !execute_ok(inode))
+			return -EACCES;
+		else
+			return 0;
+	} else /* file mode might have been restricted at mount time
 		on the client (above and beyond ACL on servers) for
 		servers which do not support setting and viewing mode bits,
 		so allowing client to check permissions is useful */

fs/coda/dir.c

···
 	if (!mask)
 		return 0; 
 
+	if ((mask & MAY_EXEC) && !execute_ok(inode))
+		return -EACCES;
+
 	lock_kernel();
 
 	if (coda_cache_check(inode, mask))

fs/coda/pioctl.c

···
 /* the coda pioctl inode ops */
 static int coda_ioctl_permission(struct inode *inode, int mask)
 {
-        return 0;
+	return (mask & MAY_EXEC) ? -EACCES : 0;
 }
 
 static int coda_pioctl(struct inode * inode, struct file * filp, 

fs/hfs/inode.c

···
 	}
 }
 
-static int hfs_permission(struct inode *inode, int mask)
-{
-	if (S_ISREG(inode->i_mode) && mask & MAY_EXEC)
-		return 0;
-	return generic_permission(inode, mask, NULL);
-}
-
 static int hfs_file_open(struct inode *inode, struct file *file)
 {
 	if (HFS_IS_RSRC(inode))
···
 	.lookup		= hfs_file_lookup,
 	.truncate	= hfs_file_truncate,
 	.setattr	= hfs_inode_setattr,
-	.permission	= hfs_permission,
 	.setxattr	= hfs_setxattr,
 	.getxattr	= hfs_getxattr,
 	.listxattr	= hfs_listxattr,

fs/hfsplus/inode.c

···
 	perms->dev = cpu_to_be32(HFSPLUS_I(inode).dev);
 }
 
-static int hfsplus_permission(struct inode *inode, int mask)
-{
-	/* MAY_EXEC is also used for lookup, if no x bit is set allow lookup,
-	 * open_exec has the same test, so it's still not executable, if a x bit
-	 * is set fall back to standard permission check.
-	 */
-	if (S_ISREG(inode->i_mode) && mask & MAY_EXEC && !(inode->i_mode & 0111))
-		return 0;
-	return generic_permission(inode, mask, NULL);
-}
-
-
 static int hfsplus_file_open(struct inode *inode, struct file *file)
 {
 	if (HFSPLUS_IS_RSRC(inode))
···
 static const struct inode_operations hfsplus_file_inode_operations = {
 	.lookup		= hfsplus_file_lookup,
 	.truncate	= hfsplus_file_truncate,
-	.permission	= hfsplus_permission,
 	.setxattr	= hfsplus_setxattr,
 	.getxattr	= hfsplus_getxattr,
 	.listxattr	= hfsplus_listxattr,

fs/namei.c

···
 	 * Read/write DACs are always overridable.
 	 * Executable DACs are overridable if at least one exec bit is set.
 	 */
-	if (!(mask & MAY_EXEC) ||
-	    (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode))
+	if (!(mask & MAY_EXEC) || execute_ok(inode))
 		if (capable(CAP_DAC_OVERRIDE))
 			return 0;
 
···
 	}
 
 	/* Ordinary permission routines do not understand MAY_APPEND. */
-	if (inode->i_op && inode->i_op->permission) {
+	if (inode->i_op && inode->i_op->permission)
 		retval = inode->i_op->permission(inode, mask);
-		if (!retval) {
-			/*
-			 * Exec permission on a regular file is denied if none
-			 * of the execute bits are set.
-			 *
-			 * This check should be done by the ->permission()
-			 * method.
-			 */
-			if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode) &&
-			    !(inode->i_mode & S_IXUGO))
-				return -EACCES;
-		}
-	} else {
+	else
 		retval = generic_permission(inode, mask, NULL);
-	}
+
 	if (retval)
 		return retval;
 

fs/nfs/dir.c

···
 	} else
 		res = PTR_ERR(cred);
 out:
+	if (!res && (mask & MAY_EXEC) && !execute_ok(inode))
+		res = -EACCES;
+
 	dfprintk(VFS, "NFS: permission(%s/%ld), mask=0x%x, res=%d\n",
 		inode->i_sb->s_id, inode->i_ino, mask, res);
 	return res;

fs/proc/proc_sysctl.c

···
 	 * sysctl entries that are not writeable,
 	 * are _NOT_ writeable, capabilities or not.
 	 */
-	struct ctl_table_header *head = grab_header(inode);
-	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
+	struct ctl_table_header *head;
+	struct ctl_table *table;
 	int error;
 
+	/* Executable files are not allowed under /proc/sys/ */
+	if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
+		return -EACCES;
+
+	head = grab_header(inode);
 	if (IS_ERR(head))
 		return PTR_ERR(head);
 
+	table = PROC_I(inode)->sysctl_entry;
 	if (!table) /* global root - r-xr-xr-x */
 		error = mask & MAY_WRITE ? -EACCES : 0;
 	else /* Use the permissions on the sysctl table entry */

include/linux/fs.h

···
 extern int generic_permission(struct inode *, int,
 		int (*check_acl)(struct inode *, int));
 
+static inline bool execute_ok(struct inode *inode)
+{
+	return (inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode);
+}
+
 extern int get_write_access(struct inode *);
 extern int deny_write_access(struct file *);
 static inline void put_write_access(struct inode * inode)