linux-kernel - Re: [PATCH][next] afs: fix a dereference on pointer cell before cell is null checked

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Date:   Tue, 27 Oct 2020 11:05:46 +0000
From:   David Howells <dhowells@...hat.com>
To:     Colin King <colin.king@...onical.com>
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] afs: fix a dereference on pointer cell before cell is null checked

Colin King <colin.king@...onical.com> wrote:

> @@ -606,7 +605,7 @@ void afs_unuse_cell(struct afs_net *net, struct afs_cell *cell, enum afs_cell_tr
>  
>  	u = atomic_read(&cell->ref);
>  	a = atomic_dec_return(&cell->active);
> -	trace_afs_cell(debug_id, u, a, reason);
> +	trace_afs_cell(cell->debug_id, u, a, reason);

It's probably better to read cell->debug_id before calling
atomic_dec_return().

I have a patch for this based on a report by Dan Carpenter, so no need to send
a revised patch.

Thanks,
David