On 2/28/11 7:03 PM, Jeffrey Hundstad wrote:
> Sadly, I didn't have the vmlinux file around anymore. I'll be glad to recreate it when I get in tomorrow. However, I have revered commit 3a3675b7f23f83ca8c67c9c2b6edf707fd28d1ba and the problem seems to have vanished. I'm guessing the stack at this point is a little to fragile for a memset. The patch is:
Ok, no worries, if the below commit is the culprit for sure, that's enough...
So, whoopsies.
STATIC int
xfs_ioc_fsgeometry_v1(
xfs_mount_t *mp,
void __user *arg)
{
xfs_fsop_geom_v1_t fsgeo;
int error;
error = xfs_fs_geometry(mp, (xfs_fsop_geom_t *)&fsgeo, 3);
what we really have is an xfs_fsop_geom_v1_t, but cast to a xfs_fsop_geom_t.
xfs_fs_geometry() zeroes it out to the tune of sizeof (xfs_fsop_geom_t)
the latter is bigger, with the addition of
__u32 logsunit;
so we overwrite memory that's not ours. :( Seems like we should zero
in the callers, when we know how much is really on the stack. I'll follow
up with a patch; pity this one was fast-tracked for security, I think :(
-Eric
>
> commit 3a3675b7f23f83ca8c67c9c2b6edf707fd28d1ba
> Author: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>
> Date: Mon Feb 14 13:45:28 2011 +0000
>
> xfs: prevent leaking uninitialized stack memory in FSGEOMETRY_V1
>
> 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.
>
> v2 switches to memset() to avoid future issues if structure members
> change, on suggestion of Dave Chinner.
>
> Signed-off-by: Dan Rosenberg <drosenberg@xxxxxxxxxxxxx>
> Reviewed-by: Eugene Teo <eugeneteo@xxxxxxxxxx>
> Signed-off-by: Alex Elder <aelder@xxxxxxx>
>
> diff --git b/fs/xfs/xfs_fsops.c a/fs/xfs/xfs_fsops.c
> index cec89dd..85668ef 100644
> --- b/fs/xfs/xfs_fsops.c
> +++ a/fs/xfs/xfs_fsops.c
> @@ -53,6 +53,9 @@ xfs_fs_geometry(
> xfs_fsop_geom_t *geo,
> int new_version)
> {
> +
> + memset(geo, 0, sizeof(*geo));
> +
> geo->blocksize = mp->m_sb.sb_blocksize;
> geo->rtextsize = mp->m_sb.sb_rextsize;
> geo->agblocks = mp->m_sb.sb_agblocks;
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