linux-kernel - Re: [PATCH linux-next] lockd: nlmsvc_mark

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Message-ID: <20130212212246.GH10267@fieldses.org>
Date:	Tue, 12 Feb 2013 16:22:46 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Tim Gardner <tim.gardner@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-nfs@...r.kernel.org
Subject: Re: [PATCH linux-next] lockd: nlmsvc_mark_resources(): avoid stack
 overflow

On Tue, Feb 12, 2013 at 12:48:58PM -0700, Tim Gardner wrote:
> Dynamically allocate the NLM host structure in order to avoid stack overflow.
> nlmsvc_mark_resources() is several call levels deep in a stack
> that has a number of large variables. 512 bytes seems like a lot
> on the stack at this point.
> 
> smatch analysis:
> 
> fs/lockd/svcsubs.c:366 nlmsvc_mark_resources() warn: 'hint' puts
>  512 bytes on stack
> 
> Cc: Trond Myklebust <Trond.Myklebust@...app.com>
> Cc: "J. Bruce Fields" <bfields@...ldses.org>
> Cc: linux-nfs@...r.kernel.org
> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> ---
>  fs/lockd/svcsubs.c |   12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/lockd/svcsubs.c b/fs/lockd/svcsubs.c
> index b904f41..f3abb7f 100644
> --- a/fs/lockd/svcsubs.c
> +++ b/fs/lockd/svcsubs.c
> @@ -363,11 +363,15 @@ nlmsvc_is_client(void *data, struct nlm_host *dummy)
>  void
>  nlmsvc_mark_resources(struct net *net)
>  {
> -	struct nlm_host hint;
> +	struct nlm_host *hint = kzalloc(sizeof(*hint), GFP_KERNEL);
>  
> -	dprintk("lockd: nlmsvc_mark_resources for net %p\n", net);
> -	hint.net = net;
> -	nlm_traverse_files(&hint, nlmsvc_mark_host, NULL);
> +	if (hint) {
> +		dprintk("lockd: nlmsvc_mark_resources for net %p\n", net);
> +		hint->net = net;
> +		nlm_traverse_files(hint, nlmsvc_mark_host, NULL);
> +	}

Silently neglecting to do this looks like a bad idea.

It's strange that we're passing in an nlm_host when all we actually use
is the struct net*.  Why not just change this to pass in the net
instead?

--b.

> +
> +	kfree(hint);
>  }
>  
>  /*
> -- 
> 1.7.9.5
> 
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