linux-kernel - Re: [PATCH 4.4 34/47] userns: move user access out of the mutex

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Date:   Sun, 9 Sep 2018 11:29:18 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Rafael David Tinoco <rafael.tinoco@...aro.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        jannh@...gle.com, christian@...uner.io, serge@...lyn.com,
        ebiederm@...ssion.com, dan.rue@...aro.org,
        naresh.kamboju@...aro.org
Subject: Re: [PATCH 4.4 34/47] userns: move user access out of the mutex

On Sun, Sep 09, 2018 at 11:16:33AM +0200, Greg KH wrote:
> On Sun, Sep 09, 2018 at 12:56:45AM -0300, Rafael David Tinoco wrote:
> > Greg,
> > 
> > On Fri, Sep 7, 2018 at 6:41 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > >
> > > ------------------
> > >
> > > From: Jann Horn <jannh@...gle.com>
> > >
> > > commit 5820f140edef111a9ea2ef414ab2428b8cb805b1 upstream.
> > >
> > > The old code would hold the userns_state_mutex indefinitely if
> > > memdup_user_nul stalled due to e.g. a userfault region. Prevent that by
> > > moving the memdup_user_nul in front of the mutex_lock().
> > >
> > > Note: This changes the error precedence of invalid buf/count/*ppos vs
> > > map already written / capabilities missing.
> > >
> > > Fixes: 22d917d80e84 ("userns: Rework the user_namespace adding uid/gid...")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Jann Horn <jannh@...gle.com>
> > > Acked-by: Christian Brauner <christian@...uner.io>
> > > Acked-by: Serge Hallyn <serge@...lyn.com>
> > > Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > >
> > > ---
> > >  kernel/user_namespace.c |   22 ++++++++++------------
> > >  1 file changed, 10 insertions(+), 12 deletions(-)
> > >
> > > --- a/kernel/user_namespace.c
> > > +++ b/kernel/user_namespace.c
> > > @@ -604,7 +604,16 @@ static ssize_t map_write(struct file *fi
> > >         struct uid_gid_extent *extent = NULL;
> > >         unsigned long page = 0;
> > >         char *kbuf, *pos, *next_line;
> > > -       ssize_t ret = -EINVAL;
> > > +       ssize_t ret;
> > > +
> > > +       /* Only allow < page size writes at the beginning of the file */
> > > +       if ((*ppos != 0) || (count >= PAGE_SIZE))
> > > +               return -EINVAL;
> > > +
> > > +       /* Slurp in the user data */
> > > +       if (copy_from_user(kbuf, buf, count))
> > > +               return -EFAULT;
> > > +       kbuf[count] = '\0';
> > 
> > Naresh will soon report issues found by LKFT on user_ns for 4.4 kernel
> > for this review round.
> > 
> > selftests: mount_run_tests.sh [FAIL]
> > write to /proc/self/uid_map failed: Bad address
> > 
> > LTP: user_namespace2 1 TBROK : safe_macros.c:452: userns02.c:95:
> > write(6,0x7ffc133113d0,18446744073709551615) failed: errno=EFAULT(14):
> > Bad address
> > 
> > I believe the EFAULT was caused because when changing code from
> > "memdup_user_nul" to "copy_from_user", for the older kernels, you
> > missed allocating the slab object for "kbuf", like memdup_user_nul()
> > does.
> > 
> > Note: This likely applies to 3.18 as well.
> > 
> > We are finishing functional tests without this patch, but we wanted to
> > make you aware right away.
> 
> Ok, should now be fixed up, thanks for finding this and noticing it.
> I've pushed out a -rc3 with the fix.

And I've fixed it up in 3.18 as well, pushing out a -rc2 with the fix.

thanks,

greg k-h