linux-kernel - Re: [PATCH v3] selinux: lsm: fix a missing-check bug in selinux_sb_eat_lsm

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Date:   Sat, 1 Jun 2019 03:34:49 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Gen Zhang <blackgod016574@...il.com>
Cc:     paul@...l-moore.com, sds@...ho.nsa.gov, eparis@...isplace.org,
        omosnace@...hat.com, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v3] selinux: lsm: fix a missing-check bug in
 selinux_sb_eat_lsm_opts()

On Sat, Jun 01, 2019 at 03:25:27AM +0100, Al Viro wrote:
> On Sat, Jun 01, 2019 at 10:15:26AM +0800, Gen Zhang wrote:
> > In selinux_sb_eat_lsm_opts(), 'arg' is allocated by kmemdup_nul(). It
> > returns NULL when fails. So 'arg' should be checked. And 'mnt_opts' 
> > should be freed when error.
> 
> What's the latter one for?  On failure we'll get to put_fs_context()
> pretty soon, so
>         security_free_mnt_opts(&fc->security);
> will be called just fine.  Leaving it allocated on failure is fine...

Actually, right now in mainline it is not (btrfs_mount_root() has
an odd call of security_sb_eat_lsm_opts()); eventually we will be
down to just the callers in ->parse_monolithic() instances, at which
point the above will become correct.  At the moment it is not, so
consider the objection withdrawn (and I really need to get some sleep,
seeing how long did it take me to recall the context... ;-/)