->permission() sanitizing: MAY_NOT_BLOCK

Duplicate the flags argument into mask bitmap.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -318,13 +318,16 @@ static inline int exec_permission(struct inode *inode, unsigned int flags)
 {
 	int ret;
 	struct user_namespace *ns = inode_userns(inode);
+	int mask = MAY_EXEC;
+	if (flags & IPERM_FLAG_RCU)
+		mask |= MAY_NOT_BLOCK;
 
 	if (inode->i_op->permission) {
-		ret = inode->i_op->permission(inode, MAY_EXEC, flags);
+		ret = inode->i_op->permission(inode, mask, flags);
 		if (likely(!ret))
 			goto ok;
 	} else {
-		ret = acl_permission_check(inode, MAY_EXEC, flags);
+		ret = acl_permission_check(inode, mask, flags);
 		if (likely(!ret))
 			goto ok;
 		if (ret != -EACCES)

fs/proc/proc_sysctl.c

@@ -316,7 +316,7 @@ static int proc_sys_permission(struct inode *inode, int mask,unsigned int flags)
 	if (!table) /* global root - r-xr-xr-x */
 		error = mask & MAY_WRITE ? -EACCES : 0;
 	else /* Use the permissions on the sysctl table entry */
-		error = sysctl_perm(head->root, table, mask);
+		error = sysctl_perm(head->root, table, mask & ~MAY_NOT_BLOCK);
 
 	sysctl_head_finish(head);
 	return error;

include/linux/fs.h

@@ -63,6 +63,7 @@ struct inodes_stat_t {
 #define MAY_ACCESS 16
 #define MAY_OPEN 32
 #define MAY_CHDIR 64
+#define MAY_NOT_BLOCK 128	/* called from RCU mode, don't block */
 
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond