[PATCH] lsm: fix default return value of the socket_getpeersec_* hooks

[Paul Moore]

On Mon, Jan 29, 2024 at 6:25 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
>
> On 1/29/2024 3:02 PM, Paul Moore wrote:
> > On Fri, Jan 26, 2024 at 1:45 PM Ondrej Mosnacek <omosnace at redhat.com> wrote:
> >> For these hooks the true "neutral" value is -EOPNOTSUPP, which is
> >> currently what is returned when no LSM provides this hook and what LSMs
> >> return when there is no security context set on the socket. Correct the
> >> value in <linux/lsm_hooks.h> and adjust the dispatch functions in
> >> security/security.c to avoid issues when the BPF LSM is enabled.
> >>
> >> Fixes: 98e828a0650f ("security: Refactor declaration of LSM hooks")
> >> Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
> >> ---
> >>  include/linux/lsm_hook_defs.h |  4 ++--
> >>  security/security.c           | 31 +++++++++++++++++++++++++++----
> >>  2 files changed, 29 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> >> index 185924c56378..76458b6d53da 100644
> >> --- a/include/linux/lsm_hook_defs.h
> >> +++ b/include/linux/lsm_hook_defs.h
> >> @@ -315,9 +315,9 @@ LSM_HOOK(int, 0, socket_getsockopt, struct socket *sock, int level, int optname)
> >>  LSM_HOOK(int, 0, socket_setsockopt, struct socket *sock, int level, int optname)
> >>  LSM_HOOK(int, 0, socket_shutdown, struct socket *sock, int how)
> >>  LSM_HOOK(int, 0, socket_sock_rcv_skb, struct sock *sk, struct sk_buff *skb)
> >> -LSM_HOOK(int, 0, socket_getpeersec_stream, struct socket *sock,
> >> +LSM_HOOK(int, -ENOPROTOOPT, socket_getpeersec_stream, struct socket *sock,
> >>          sockptr_t optval, sockptr_t optlen, unsigned int len)
> >> -LSM_HOOK(int, 0, socket_getpeersec_dgram, struct socket *sock,
> >> +LSM_HOOK(int, -ENOPROTOOPT, socket_getpeersec_dgram, struct socket *sock,
> >>          struct sk_buff *skb, u32 *secid)
> >>  LSM_HOOK(int, 0, sk_alloc_security, struct sock *sk, int family, gfp_t priority)
> >>  LSM_HOOK(void, LSM_RET_VOID, sk_free_security, struct sock *sk)
> >> diff --git a/security/security.c b/security/security.c
> >> index 6196ccaba433..3aaad75c9ce8 100644
> >> --- a/security/security.c
> >> +++ b/security/security.c
> >> @@ -4624,8 +4624,20 @@ EXPORT_SYMBOL(security_sock_rcv_skb);
> >>  int security_socket_getpeersec_stream(struct socket *sock, sockptr_t optval,
> >>                                       sockptr_t optlen, unsigned int len)
> >>  {
> >> -       return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock,
> >> -                            optval, optlen, len);
> >> +       struct security_hook_list *hp;
> >> +       int rc;
> >> +
> >> +       /*
> >> +        * Only one module will provide a security context.
> >> +        */
> >> +       hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream,
> >> +                            list) {
> >> +               rc = hp->hook.socket_getpeersec_stream(sock, optval, optlen,
> >> +                                                      len);
> >> +               if (rc != LSM_RET_DEFAULT(socket_getpeersec_stream))
> >> +                       return rc;
> >> +       }
> >> +       return LSM_RET_DEFAULT(socket_getpeersec_stream);
> >>  }
> >
> > I'm beginning to wonder if we shouldn't update call_int_hook() so that
> > it works for LSM_RET_DEFAULT() instead of assuming a zero/0 return
> > value.  Thoughts?
>
> call_int_hook() was intended to address the "normal" case, where all
> hooks registered would be called and the first error, if any, would
> result in an immediate failure return. Hooks that behaved in any other
> manner were expected to be open coded. The point of using the macros
> was to reduce so much code duplication. I really don't want to see
> call_int_hook() evolve into something hard to work with, or that has
> non-obvious side effects. I think we could probably integrate
> LSM_RET_DEFAULT() safely, but I'm wary of hiding these abnormal cases
> in the macro.

Yes, I'm not talking about modifying call_int_hook() to handle
something like security_vm_enough_memory_mm(), I'm just talking about
updating it use LSM_RET_DEFAULT() instead of zero.

While we are at it, we should probably get rid of the second parameter
too, @IRC, and just use the assigned LSM_RET_DEFAULT().  That always
struck me as a bug waiting to happen if/when those two fell out of
sync.

--
paul-moore.com