[PATCH v2] LSM: general protection fault in legacy_parse_param

[Paul Moore]

On Thu, Jan 27, 2022 at 12:46 PM James Morris <jmorris at namei.org> wrote:
> On Thu, 27 Jan 2022, Casey Schaufler wrote:
>
> > The usual LSM hook "bail on fail" scheme doesn't work for cases where
> > a security module may return an error code indicating that it does not
> > recognize an input.  In this particular case Smack sees a mount option
> > that it recognizes, and returns 0. A call to a BPF hook follows, which
> > returns -ENOPARAM, which confuses the caller because Smack has processed
> > its data.
> >
> > The SELinux hook incorrectly returns 1 on success. There was a time
> > when this was correct, however the current expectation is that it
> > return 0 on success. This is repaired.
> >
> > Reported-by: syzbot+d1e3b1d92d25abf97943 at syzkaller.appspotmail.com
> > Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
>
>
> Acked-by: James Morris <jamorris at linux.microsoft.com>

Looks good to me too, thanks Casey.  Since James' already ACK'd it, I
went ahead and pulled this into selinux/next.

> > ---
> >  security/security.c      | 17 +++++++++++++++--
> >  security/selinux/hooks.c |  5 ++---
> >  2 files changed, 17 insertions(+), 5 deletions(-)
> >
> > diff --git a/security/security.c b/security/security.c
> > index 3d4eb474f35b..e649c8691be2 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -884,9 +884,22 @@ int security_fs_context_dup(struct fs_context *fc, struct
> > fs_context *src_fc)
> >       return call_int_hook(fs_context_dup, 0, fc, src_fc);
> >  }
> >
> > -int security_fs_context_parse_param(struct fs_context *fc, struct
> > fs_parameter *param)
> > +int security_fs_context_parse_param(struct fs_context *fc,
> > +                                 struct fs_parameter *param)
> >  {
> > -     return call_int_hook(fs_context_parse_param, -ENOPARAM, fc, param);
> > +     struct security_hook_list *hp;
> > +     int trc;
> > +     int rc = -ENOPARAM;
> > +
> > +     hlist_for_each_entry(hp, &security_hook_heads.fs_context_parse_param,
> > +                          list) {
> > +             trc = hp->hook.fs_context_parse_param(fc, param);
> > +             if (trc == 0)
> > +                     rc = 0;
> > +             else if (trc != -ENOPARAM)
> > +                     return trc;
> > +     }
> > +     return rc;
> >  }
> >
> >  int security_sb_alloc(struct super_block *sb)
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 5b6895e4fc29..371f67a37f9a 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -2860,10 +2860,9 @@ static int selinux_fs_context_parse_param(struct
> > fs_context *fc,
> >               return opt;
> >
> >       rc = selinux_add_opt(opt, param->string, &fc->security);
> > -     if (!rc) {
> > +     if (!rc)
> >               param->string = NULL;
> > -             rc = 1;
> > -     }
> > +
> >       return rc;
> >  }

-- 
paul-moore.com