linux-kernel - Re: Linux 3.18.111

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Date:   Fri, 10 Aug 2018 12:11:58 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Seung-Woo Kim <sw0312.kim@...sung.com>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable <stable@...r.kernel.org>, lwn@....net,
        Jiri Slaby <jslaby@...e.cz>
Subject: Re: Linux 3.18.111

On Fri, Aug 10, 2018 at 03:43:02PM +0900, Seung-Woo Kim wrote:
> On 2018년 08월 08일 19:06, Seung-Woo Kim wrote:
> > On 2018년 07월 05일 09:52, Al Viro wrote:
> >> On Mon, Jul 02, 2018 at 10:01:25PM -0700, Linus Torvalds wrote:
> >>> On Mon, Jul 2, 2018 at 9:43 PM Seung-Woo Kim <sw0312.kim@...sung.com> wrote:
> >>>>
> >>>> I think the commit itself is required. Simple, but not reliable,
> >>>> workaround fix is like below:
> >>>>
> >>>> diff --git a/fs/dcache.c b/fs/dcache.c
> >>>> index a34d401..7c751f2 100644
> >>>> --- a/fs/dcache.c
> >>>> +++ b/fs/dcache.c
> >>>> @@ -1879,6 +1879,8 @@ void d_instantiate_new(struct dentry *entry,
> >>>> struct inode *inode)
> >>>>         BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
> >>>>         BUG_ON(!inode);
> >>>>         lockdep_annotate_inode_mutex_key(inode);
> >>>> +       /* WORKAROUND for calling security_d_instantiate() */
> >>>> +       entry->d_inode = inode;
> >>>>         security_d_instantiate(entry, inode);
> >>>>         spin_lock(&inode->i_lock);
> >>>>         __d_instantiate(entry, inode);
> >>>
> >>> Ugh. That looks horrible even if it might avoid the oops.
> >>>
> >>> I think a much better solution is to back-port commit b296821a7c42
> >>> ("xattr_handler: pass dentry and inode as separate arguments of
> >>> ->get()") to older kernels. Then the inode is passed down all the way,
> >>> and you don't have people try to get it from the (not yet initialized)
> >>> dentry.
> >>>
> >>> But there might be other parts missing too, and I didn't look at how
> >>> easy/painful that backport would be.
> >>>
> >>> Al - comments? This is all because of commit 1e2e547a93a0 ("do
> >>> d_instantiate/unlock_new_inode combinations safely") being marked for
> >>> stable, and various cases of security_d_instantiate() calling down to
> >>> getxattr. Which used to not get the inode at all, so those older
> >>> kernels use d_inode(dentry), which doesn't work in this path since
> >>> dentry->d_inode hasn't been instantiated yet..
> >>
> >> You also want b96809173e94 and ce23e6401334 there...
> > 
> > For above two commits, also b296821a7c42 is required. And after
> > backport, smack still crashed because setxattr. To fix it, 5930122683df
> > and 3767e255b390 are also required.
> > 
> > By the way, does no one have met this kind getxattr crash issue with
> > selinux from 3.18.y?
> > 
> 
> I have checked with selinux, and it is confirmed that there is no crash
> because selinux_d_instantiate() has null check for inode. So, it is only
> security smack issue.

So are the 5 patches you sent ok to apply to the 3.18-stable tree?  Or
do we need to do something else?

thanks,

greg k-h