Re: [fuse-devel] [PATCH] fuse: mark all aliases of an inode stale in unlink

[Miklos S. <mi...@sz...>]

Anand Avati <av...@re...> writes:

> Problem:
> 	create("filename") => 0
> 	link("filename", "linkname") => 0
> 	unlink("filename") => 0
> 	link("linkname", "filename") => -ENOENT ### BUG ###
>
> This is a test case link section of the Poix compliance test suite from
> ntfs-3g project.
>
> Cause:
> 	fuse_unlink() clears i_nlink of the inode. If the inode has
> hardlinks (and hence aliases) they kept fresh (within the entry
> timeout bounds.) A link() call happening right after unlink now checks
> for i_nlink == 0 (since patch aae8a97d3ec30788790d1720b71d76fd8eb44b73)
> and fails the syscall for security reasons.
>
> Fix:
> 	Instead of marking the just-unlinked entry as stale, mark all
> the aliases as stale so that a revalidation of the alias is done during
> path resolution.

This is only a partial fix: the entry may still be referenced and used:
linkat(..., AT_EMPTY_PATH).  There are also several other places where
i_nlink is cheked without refreshing the attributes.

So how about changing that clear_nlink() to drop_nlink()?

I don't quite understand what that comment above clear_nlink() is saying
but I suspect it comes from before ->drop_inode was used.  Now the inode
will go away if no dentry is referencing it regardless of the value of
i_nlink.

Untested patch below.  Does that work for you?

Thanks,
Miklos


diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 2066328..517a7f5 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -645,12 +645,7 @@ static int fuse_unlink(struct inode *dir, struct dentry *entry)
 	if (!err) {
 		struct inode *inode = entry->d_inode;
 
-		/*
-		 * Set nlink to zero so the inode can be cleared, if the inode
-		 * does have more links this will be discovered at the next
-		 * lookup/getattr.
-		 */
-		clear_nlink(inode);
+		drop_nlink(inode);
 		fuse_invalidate_attr(inode);
 		fuse_invalidate_attr(dir);
 		fuse_invalidate_entry_cache(entry);