linux-kernel - Re: [PATCH] fs: fix NULL dereference due to data race in prepend

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Message-ID: <CAHk-=wiE04vsfJmZ-AyWJHfNdGa=WmBYt4bP3aN+sTP05=QXXA@mail.gmail.com>
Date:   Wed, 14 Oct 2020 14:49:18 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrii Nakryiko <andrii@...nel.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        kernel-team@...com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: fix NULL dereference due to data race in prepend_path()

On Wed, Oct 14, 2020 at 2:40 PM Andrii Nakryiko <andrii@...nel.org> wrote:
>
> Fix data race in prepend_path() with re-reading mnt->mnt_ns twice without
> holding the lock. is_mounted() does check for NULL, but is_anon_ns(mnt->mnt_ns)
> might re-read the pointer again which could be NULL already, if in between
> reads one of kern_unmount()/kern_unmount_array()/umount_tree() sets mnt->mnt_ns
> to NULL.

This seems like the obviously correct fix, so I think I'll just apply
it directly.

Al? Holler if you have any issues with this..

             Linus