[PATCH 6/6] efivarfs: fix error on write to new variable leaving remnants

[James Bottomley <James.Bottomley@HansenPartnership.com>]

Make variable cleanup go through the fops release mechanism and use
zero inode size as the indicator to delete the file.  Since all EFI
variables must have an initial u32 attribute, zero size occurs either
because the update deleted the variable or because an unsuccessful
write after create caused the size never to be set in the first place.

Even though this fixes the bug that a create either not followed by a
write or followed by a write that errored would leave a remnant file
for the variable, the file will appear momentarily globally visible
until the close of the fd deletes it.  This is safe because the normal
filesystem operations will mediate any races; however, it is still
possible for a directory listing at that instant between create and
close contain a variable that doesn't exist in the EFI table.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 fs/efivarfs/file.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c
index 23c51d62f902..edf363f395f5 100644
--- a/fs/efivarfs/file.c
+++ b/fs/efivarfs/file.c
@@ -38,22 +38,24 @@ static ssize_t efivarfs_file_write(struct file *file,
 
 	bytes = efivar_entry_set_get_size(var, attributes, &datasize,
 					  data, &set);
-	if (!set && bytes) {
+	if (!set) {
 		if (bytes == -ENOENT)
 			bytes = -EIO;
 		goto out;
 	}
 
+	inode_lock(inode);
 	if (bytes == -ENOENT) {
-		drop_nlink(inode);
-		d_delete(file->f_path.dentry);
-		dput(file->f_path.dentry);
+		/*
+		 * zero size signals to release that the write deleted
+		 * the variable
+		 */
+		i_size_write(inode, 0);
 	} else {
-		inode_lock(inode);
 		i_size_write(inode, datasize + sizeof(attributes));
 		inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
-		inode_unlock(inode);
 	}
+	inode_unlock(inode);
 
 	bytes = count;
 
@@ -106,8 +108,19 @@ static ssize_t efivarfs_file_read(struct file *file, char __user *userbuf,
 	return size;
 }
 
+static int efivarfs_file_release(struct inode *inode, struct file *file)
+{
+	if (i_size_read(inode) == 0) {
+		drop_nlink(inode);
+		d_delete(file->f_path.dentry);
+		dput(file->f_path.dentry);
+	}
+	return 0;
+}
+
 const struct file_operations efivarfs_file_operations = {
-	.open	= simple_open,
-	.read	= efivarfs_file_read,
-	.write	= efivarfs_file_write,
+	.open		= simple_open,
+	.read		= efivarfs_file_read,
+	.write		= efivarfs_file_write,
+	.release	= efivarfs_file_release,
 };
-- 
2.35.3