fix execute checking in permission()

permission() checks that MAY_EXEC is only allowed on regular files if at least
one execute bit is set in the file mode.

generic_permission() already ensures this, so the extra check in permission()
is superfluous.

If the filesystem defines it's own ->permission() the check may still be
needed.  In this case move it after ->permission().  This is needed because
filesystems such as FUSE may need to refresh the inode attributes before
checking permissions.

This check should be moved inside ->permission(), but that's another story.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/namei.c

@@ -227,10 +227,10 @@ int generic_permission(struct inode *inode, int mask,
 
 int permission(struct inode *inode, int mask, struct nameidata *nd)
 {
-	umode_t mode = inode->i_mode;
 	int retval, submask;
 
 	if (mask & MAY_WRITE) {
+		umode_t mode = inode->i_mode;
 
 		/*
 		 * Nobody gets write access to a read-only fs.
@@ -246,22 +246,34 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
 			return -EACCES;
 	}
 
-
-	/*
-	 * MAY_EXEC on regular files requires special handling: We override
-	 * filesystem execute permissions if the mode bits aren't set or
-	 * the fs is mounted with the "noexec" flag.
-	 */
-	if ((mask & MAY_EXEC) && S_ISREG(mode) && (!(mode & S_IXUGO) ||
-			(nd && nd->mnt && (nd->mnt->mnt_flags & MNT_NOEXEC))))
-		return -EACCES;
+	if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode)) {
+		/*
+		 * MAY_EXEC on regular files is denied if the fs is mounted
+		 * with the "noexec" flag.
+		 */
+		if (nd && nd->mnt && (nd->mnt->mnt_flags & MNT_NOEXEC))
+			return -EACCES;
+	}
 
 	/* Ordinary permission routines do not understand MAY_APPEND. */
 	submask = mask & ~MAY_APPEND;
-	if (inode->i_op && inode->i_op->permission)
+	if (inode->i_op && inode->i_op->permission) {
 		retval = inode->i_op->permission(inode, submask, nd);
-	else
+		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 {
 		retval = generic_permission(inode, submask, NULL);
+	}
 	if (retval)
 		return retval;