linux-kernel - Re: [PATCH 3/4] fs, afs: convert afs_server.usage from atomic_t to refcount

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Message-ID: <483.1487781128@warthog.procyon.org.uk>
Date:   Wed, 22 Feb 2017 16:32:08 +0000
From:   David Howells <dhowells@...hat.com>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     dhowells@...hat.com, linux-kernel@...r.kernel.org,
        linux-afs@...ts.infradead.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 3/4] fs, afs: convert afs_server.usage from atomic_t to refcount_t

Elena Reshetova <elena.reshetova@...el.com> wrote:

> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.

Although I don't see an assertion for this (the window is too small), it is
possible for a dead server record to get resurrected.  Take a look at
afs_put_server() and note there's a check around the move to the graveyard.

So, please hold this patch also.

David