linux-kernel - Re: KASAN: use-after-free Read in path

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Message-ID: <20190410181135.GA32071@ZenIV.linux.org.uk>
Date:   Wed, 10 Apr 2019 19:11:35 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     syzbot <syzbot+7a8ba368b47fdefca61e@...kaller.appspotmail.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        James Morris <jmorris@...ei.org>,
        linux-security-module@...r.kernel.org
Subject: Re: KASAN: use-after-free Read in path_lookupat

On Tue, Mar 26, 2019 at 01:45:52AM +0000, Al Viro wrote:
> On Mon, Mar 25, 2019 at 11:37:32PM +0000, Al Viro wrote:
> 
> > For debugfs it's clearly "use default ->evict_inode(), have explicit
> > ->destroy_inode() using free_inode_nonrcu()" - there we have nothing
> > else done in ->evict_inode() and kfree is obviously safe in softirq.
> > I'll post that (or push to vfs.git#fixes), along with minimal fixes
> > for other 3.  If bpf_any_put() is softirq-safe, we'll have the full
> > set for -stable and the rest could be done on top of that.
> > 
> > Won't solve the documetation problem, unfortunately ;-/
> 
> Posted; all of those (as well as Daniel's bpf patch) are Cc:stable
> fodder.  Documentation is still, er, deficient...

... and unfortunately there are two more, exactly like debugfs -
securityfs and apparmorfs, found while sorting out the series
for separate rcu-delayed counterpart of ->destroy_inode().

Both are in vfs.git#fixes.  Which way should that go - directly or
via linux-security.git?  Both are stable fodder, in theory, but
much harder to hit than their ubifs/debugfs/bpf counterparts...