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From: Dave Chinner <>
To: Dan Rosenberg <>
Subject: Re: [PATCH] xfs: prevent leaking uninitialized stack memory in FSGEOMETRY_V1
Date: Mon, 14 Feb 2011 22:46:29 +1100	[thread overview]
Message-ID: <20110214114629.GA13052@dastard> (raw)
In-Reply-To: <1297347904.13370.9.camel@dan>

On Thu, Feb 10, 2011 at 09:25:04AM -0500, Dan Rosenberg wrote:
> The FSGEOMETRY_V1 ioctl (and its compat equivalent) calls out to
> xfs_fs_geometry() with a version number of 3.  This code path does not
> fill in the logsunit member of the passed xfs_fsop_geom_t, leading to
> the leaking of four bytes of uninitialized stack data to potentially
> unprivileged callers.  Since all other members are filled in all code
> paths and there are no padding bytes in this structure, it's safe to
> avoid an expensive memset() in favor of just clearing this one field.

If this really is a security problem, then it should use a memset.
This is not a performance critical path and there are differences in
the padding of the structure between 32 bit and 64 bit ioctl
variants (it has a compat ioctl handler) and that can only be
correctly handled by memset().

Also, using a memset means we won't have the problem of introducing
new uninitialised fields or padding if we ever rev the structure


Dave Chinner

  parent reply	other threads:[~2011-02-14 11:46 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-10 14:25 Dan Rosenberg
2011-02-14  8:41 ` [Security] " Eugene Teo
2011-02-14 11:46 ` Dave Chinner [this message]
2011-02-14 13:45   ` [PATCH v2] " Dan Rosenberg
2011-02-14 23:39     ` Eugene Teo

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