VFS: Fix access("file", X_OK) in the presence of ACLs

Currently, the access() call will return incorrect information on NFS if
there exists an ACL that grants execute access to the user on a regular
file. The reason the information is incorrect is that the VFS overrides
this execute access in open_exec() by checking (inode->i_mode & 0111).

This patch propagates the VFS execute bit check back into the generic
permission() call.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
(cherry picked from 64cbae98848c4c99851cb0a405f0b4982cd76c1e commit)

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.
@@ -247,6 +247,13 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
 	}
 
 
+	/*
+	 * MAY_EXEC on regular files requires special handling: We override
+	 * filesystem execute permissions if the mode bits aren't set.
+	 */
+	if ((mask & MAY_EXEC) && S_ISREG(mode) && !(mode & S_IXUGO))
+		return -EACCES;
+
 	/* Ordinary permission routines do not understand MAY_APPEND. */
 	submask = mask & ~MAY_APPEND;
 	if (inode->i_op && inode->i_op->permission)