2019-08-30 05:38:19

by Austin Kim

Subject: [PATCH] xfs: Initialize label array properly

In case kernel stack variable is not initialized properly,
there is a risk of kernel information disclosure.

So, initialize 'char label[]' array with null characters.

Signed-off-by: Austin Kim <[email protected]>
---
fs/xfs/xfs_ioctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 9ea5166..09b3bee 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -2037,7 +2037,7 @@ xfs_ioc_setlabel(
char __user *newlabel)
{
struct xfs_sb *sbp = &mp->m_sb;
- char label[XFSLABEL_MAX + 1];
+ char label[XFSLABEL_MAX + 1] = {0};
size_t len;
int error;

--
2.6.2

2019-08-30 05:41:31

by Darrick J. Wong

Subject: Re: [PATCH] xfs: Initialize label array properly

On Fri, Aug 30, 2019 at 02:37:07PM +0900, Austin Kim wrote:
> In case kernel stack variable is not initialized properly,
> there is a risk of kernel information disclosure.
>
> So, initialize 'char label[]' array with null characters.

Got a testcase for this? At least a couple other filesystems implement
this ioctl too, which means they all should be checked/tested on a
regular basis.

--D

> Signed-off-by: Austin Kim <[email protected]>
> ---
> fs/xfs/xfs_ioctl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 9ea5166..09b3bee 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -2037,7 +2037,7 @@ xfs_ioc_setlabel(
> char __user *newlabel)
> {
> struct xfs_sb *sbp = &mp->m_sb;
> - char label[XFSLABEL_MAX + 1];
> + char label[XFSLABEL_MAX + 1] = {0};
> size_t len;
> int error;
>
> --
> 2.6.2
>

2019-08-30 07:33:33

by Dave Chinner

Subject: Re: [PATCH] xfs: Initialize label array properly

On Fri, Aug 30, 2019 at 02:37:07PM +0900, Austin Kim wrote:
> In case kernel stack variable is not initialized properly,
> there is a risk of kernel information disclosure.
>
> So, initialize 'char label[]' array with null characters.

Can you describe the information disclosure vector here? I can't see
any, mostly because this is the "set label" function and that
doesn't return anything to userspace.

We also zero the on-disk label before we copy the user label into
it, so I don't see that anything can leak onto disk, either...

Cheers,

Dave.
--
Dave Chinner
[email protected]

2019-08-30 14:54:31

by Austin Kim

Subject: Re: [PATCH] xfs: Initialize label array properly

2019년 8월 30일 (금) 오후 2:39, Darrick J. Wong <[email protected]>님이 작성:
>
> On Fri, Aug 30, 2019 at 02:37:07PM +0900, Austin Kim wrote:
> > In case kernel stack variable is not initialized properly,
> > there is a risk of kernel information disclosure.
> >
> > So, initialize 'char label[]' array with null characters.
>
> Got a testcase for this? At least a couple other filesystems implement
> this ioctl too, which means they all should be checked/tested on a
> regular basis.

Thanks for feedback.
As you pointed out, I figured out ioctl(e.g: ext4_ioctl, f2fs_ioctl)
of other file system is implemented with the same ways.
Please ignore the patch in this mail thread.

BR,
Austin Kim

>
> --D
>
> > Signed-off-by: Austin Kim <[email protected]>
> > ---
> > fs/xfs/xfs_ioctl.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > index 9ea5166..09b3bee 100644
> > --- a/fs/xfs/xfs_ioctl.c
> > +++ b/fs/xfs/xfs_ioctl.c
> > @@ -2037,7 +2037,7 @@ xfs_ioc_setlabel(
> > char __user *newlabel)
> > {
> > struct xfs_sb *sbp = &mp->m_sb;
> > - char label[XFSLABEL_MAX + 1];
> > + char label[XFSLABEL_MAX + 1] = {0};
> > size_t len;
> > int error;
> >
> > --
> > 2.6.2
> >