scoutfs: provide ->permission

We need to lock and refresh the VFS inode before it checks permissions in
system calls, otherwise we risk checking against stale inode metadata.

Signed-off-by: Mark Fasheh <mfasheh@versity.com>
[zab: adapted to newer lock call]
Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/dir.c

@@ -19,6 +19,7 @@
 #include <linux/namei.h>
 
 #include "format.h"
+#include "file.h"
 #include "dir.h"
 #include "inode.h"
 #include "ioctl.h"
@@ -1131,6 +1132,7 @@ const struct inode_operations scoutfs_dir_iops = {
 	.listxattr	= scoutfs_listxattr,
 	.removexattr	= scoutfs_removexattr,
 	.symlink	= scoutfs_symlink,
+	.permission	= scoutfs_permission,
 };
 
 void scoutfs_dir_exit(void)

kmod/src/file.c

@@ -83,3 +83,24 @@ out:
 
 	return ret;
 }
+
+int scoutfs_permission(struct inode *inode, int mask)
+{
+	struct super_block *sb = inode->i_sb;
+	struct scoutfs_lock *inode_lock = NULL;
+	int ret;
+
+	if (mask & MAY_NOT_BLOCK)
+		return -ECHILD;
+
+	ret = scoutfs_lock_inode(sb, DLM_LOCK_PR, SCOUTFS_LKF_REFRESH_INODE,
+				 inode, &inode_lock);
+	if (ret)
+		return ret;
+
+	ret = generic_permission(inode, mask);
+
+	scoutfs_unlock(sb, inode_lock, DLM_LOCK_PR);
+
+	return ret;
+}

kmod/src/file.h

@@ -5,5 +5,6 @@ ssize_t scoutfs_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 			      unsigned long nr_segs, loff_t pos);
 ssize_t scoutfs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 			       unsigned long nr_segs, loff_t pos);
+int scoutfs_permission(struct inode *inode, int mask);
 
 #endif	/* _SCOUTFS_FILE_H_ */