linux-kernel - Re: [PATCH] afs: Fix clearance of reply

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Message-ID: <20181015140255.GA3510@kroah.com>
Date:   Mon, 15 Oct 2018 16:02:55 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     David Howells <dhowells@...hat.com>
Cc:     torvalds@...ux-foundation.org, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] afs: Fix clearance of reply

On Mon, Oct 15, 2018 at 12:43:02PM +0100, David Howells wrote:
> The recent patch to fix the afs_server struct leak didn't actually fix the
> bug, but rather fixed some of the symptoms.  The problem is that an
> asynchronous call that holds a resource pointed to by call->reply[0] will
> find the pointer cleared in the call destructor, thereby preventing the
> resource from being cleaned up.
> 
> In the case of the server record leak, the afs_fs_get_capabilities()
> function in devel code sets up a call with reply[0] pointing at the server
> record that should be altered when the result is obtained, but this was
> being cleared before the destructor was called, so the put in the
> destructor does nothing and the record is leaked.
> 
> Commit f014ffb025c1 removed the additional ref obtained by
> afs_install_server(), but the removal of this ref is actually used by the
> garbage collector to mark a server record as being defunct after the record
> has expired through lack of use.
> 
> The offending clearance of call->reply[0] upon completion in
> afs_process_async_call() has been there from the origin of the code, but
> none of the asynchronous calls actually use that pointer currently, so it
> should be safe to remove (note that synchronous calls don't involve this
> function).
> 
> Fix this by the following means:
> 
>  (1) Revert commit f014ffb025c1.
> 
>  (2) Remove the clearance of reply[0] from afs_process_async_call().
> 
> Without this, afs_manage_servers() will suffer an assertion failure if it
> sees a server record that didn't get used because the usage count is not 1.
> 
> Fixes: f014ffb025c1 ("afs: Fix afs_server struct leak")
> Fixes: 08e0e7c82eea ("[AF_RXRPC]: Make the in-kernel AFS filesystem use AF_RXRPC.")
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---

Now applied, thanks.

greg k-h