linux-kernel - Re: [PATCH] dcache: don't expose uninitialized memory in /proc/<pid>/fd/<fd>

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Message-Id: <20071017153201.d4e0679b.akpm@linux-foundation.org>
Date:	Wed, 17 Oct 2007 15:32:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	linux-kernel@...r.kernel.org, viro@....linux.org.uk
Subject: Re: [PATCH] dcache: don't expose uninitialized memory in
 /proc/<pid>/fd/<fd>

On Tue, 16 Oct 2007 15:35:57 -0400
"J. Bruce Fields" <bfields@...ldses.org> wrote:

> From: J. Bruce Fields <bfields@...i.umich.edu>
> 
> Well, it's not especially important that target->d_iname get the
> contents of dentry->d_iname, but it's important that it get initialized
> with *something*, otherwise we're just exposing some random piece of
> memory to anyone who reads the link at /proc/<pid>/fd/<fd> for the
> deleted file, when it's still held open by someone.
> 

hm, that was tricky.

> ---
>  fs/dcache.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> (Am I missing something?  I've also run a test program that copies a
> short (<36 character) name ontop of a long (>=36 character) name and see
> that the first time I run it, without this patch, I get unpredicatable
> results out of /proc/<pid>/fd/<fd>.)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 5663a31..24252fc 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1483,6 +1483,8 @@ static void switch_names(struct dentry *dentry, struct dentry *target)
>  			 * dentry:internal, target:external.  Steal target's
>  			 * storage and make target internal.
>  			 */
> +			memcpy(target->d_iname, dentry->d_name.name,
> +					dentry->d_name.len + 1);
>  			dentry->d_name.name = target->d_name.name;
>  			target->d_name.name = target->d_iname;
>  		}

Or we could just stick a \0 in there.

Or perhaps we should set it to "(deleted file)"?
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