Re: [PATCH] ceph: fail the open_by_handle_at() if the dentry is being unlinked

[Xiubo Li <xiubli@redhat.com>]

On 9/7/23 00:58, Sebastian Hasler wrote:
> While reviewing the implementation of __fh_to_dentry (in the CephFS 
> client), I noticed a possible race condition.
>
> Linux has a syscall linkat(2) which allows, given an open file 
> descriptor, to create a link for the file. So an inode that is 
> unlinked can become linked.
>
> Now the problem: The line ((inode->i_nlink == 0) && 
> !__ceph_is_file_opened(ci)) performs two checks. If, in between those 
> checks, the file goes from the unlinked and open state to the linked 
> and closed state, then we return -ESTALE even though the inode is 
> linked. I don't think this is the intended behavior. I guess this 
> (going from unlinked and open to linked and closed) can happen when a 
> concurrent process calls linkat() and then close().
>
Hi Sebastian,

Thanks for your reporting.

int linkat(int olddirfd, const char *oldpath, int newdirfd, const char 
*newpath, int flags);

BTW, for "an open file descripter", do you mean "olddirfd" ? Because 
"olddirfd" is a dir's open file descripter, how is that possible it can 
become linked again ?

Correct me if I'm misreading it.

Thanks

- Xiubo