Re: [PATCH] dcache: don't expose uninitialized memory in /proc//fd/

J. Bruce Fields
2007-10-22T18:08:47Z

Sorry for the delayed response:

On Wed, Oct 17, 2007 at 03:32:01PM -0700, Andrew Morton wrote:
> On Tue, 16 Oct 2007 15:35:57 -0400
> "J. Bruce Fields" <bfields@fieldses.org> wrote:
>
> > From: J. Bruce Fields <bfields@citi.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.

The memcpy() makes the behavior agree with the code comments, and with
what the kernel normally otherwise does. But, yeah, just making it a
null string would probably be reasonable too.

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

Looks like __d_path already adds a (deleted) for us, so that'de be
redundant.

--b.