From: Stephen Smalley <stephen.smalley.work@gmail.com>
To: David Howells <dhowells@redhat.com>
Cc: Paul Moore <paul@paul-moore.com>,
keyrings@vger.kernel.org, SElinux list <selinux@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms [v2]
Date: Tue, 28 Apr 2020 10:32:37 -0400 [thread overview]
Message-ID: <CAEjxPJ5+DtZfX36OLYiLbU=1tGZcPUWFUi1=mFfx=ntehtvd3Q@mail.gmail.com> (raw)
In-Reply-To: <924658.1588078484@warthog.procyon.org.uk>
On Tue, Apr 28, 2020 at 8:54 AM David Howells <dhowells@redhat.com> wrote:
>
> selinux: Fix use of KEY_NEED_* instead of KEY__* perms
>
> selinux_key_permission() is passing the KEY_NEED_* permissions to
> avc_has_perm() instead of the KEY__* values. It happens to work because
> the values are all coincident.
>
> Fixes: d720024e94de ("[PATCH] selinux: add hooks for key subsystem")
> Reported-by: Paul Moore <paul@paul-moore.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> security/selinux/hooks.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 0b4e32161b77..4b6624e5dab4 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -6539,20 +6539,39 @@ static void selinux_key_free(struct key *k)
> kfree(ksec);
> }
>
> +static unsigned int selinux_keyperm_to_av(unsigned int need_perm)
> +{
> + switch (need_perm) {
> + case KEY_NEED_VIEW: return KEY__VIEW;
> + case KEY_NEED_READ: return KEY__READ;
> + case KEY_NEED_WRITE: return KEY__WRITE;
> + case KEY_NEED_SEARCH: return KEY__SEARCH;
> + case KEY_NEED_LINK: return KEY__LINK;
> + case KEY_NEED_SETATTR: return KEY__SETATTR;
> + default:
> + WARN_ON(1);
> + return 0;
> + }
> +}
> +
> static int selinux_key_permission(key_ref_t key_ref,
> const struct cred *cred,
> - unsigned perm)
> + unsigned need_perm)
> {
> struct key *key;
> struct key_security_struct *ksec;
> + unsigned int perm;
> u32 sid;
>
> /* if no specific permissions are requested, we skip the
> permission check. No serious, additional covert channels
> appear to be created. */
> - if (perm == 0)
> + if (need_perm == 0)
> return 0;
>
> + perm = selinux_keyperm_to_av(need_perm);
> + if (perm == 0)
> + return -EPERM;
> sid = cred_sid(cred);
>
> key = key_ref_to_ptr(key_ref);
1) Are we guaranteed that the caller only ever passes a single
KEY_NEED_* perm at a time (i.e. hook is never called with a bitmask
of multiple permissions)? Where is that guarantee enforced?
2) We had talked about adding a BUILD_BUG_ON() or other build-time
guard to ensure that new KEY_NEED_* permissions
are not added without updating SELinux. We already have similar
constructs for catching new capabilities (#if CAP_LAST_CAP > 63 #error
...), socket address families (#if PF_MAX > 45 #error ...), RTM_* and
XFRM_MSG* values.
next prev parent reply other threads:[~2020-04-28 14:32 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-17 15:48 Problem with 9ba09998baa9 ("selinux: Implement the watch_key security hook") in linux-next Paul Moore
2020-04-17 16:32 ` Richard Haines
2020-04-17 16:59 ` Paul Moore
2020-04-21 12:29 ` David Howells
2020-04-22 19:20 ` Paul Moore
2020-04-22 21:09 ` Paul Moore
2020-04-24 23:43 ` David Howells
2020-04-26 20:53 ` Paul Moore
2020-04-27 14:12 ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms David Howells
2020-04-27 14:36 ` Stephen Smalley
2020-04-27 15:24 ` Paul Moore
2020-04-27 17:02 ` Stephen Smalley
2020-04-27 22:17 ` Paul Moore
2020-04-28 12:54 ` [PATCH] selinux: Fix use of KEY_NEED_* instead of KEY__* perms [v2] David Howells
2020-04-28 14:32 ` Stephen Smalley [this message]
2020-04-28 15:57 ` David Howells
2020-04-28 16:19 ` Stephen Smalley
2020-05-01 16:37 ` Paul Moore
2020-05-12 22:33 ` [PATCH] keys: Make the KEY_NEED_* perms an enum rather than a mask David Howells
2020-05-13 1:04 ` Paul Moore
2020-05-13 12:58 ` Stephen Smalley
2020-05-13 15:25 ` Casey Schaufler
2020-05-13 23:13 ` David Howells
2020-05-14 12:08 ` Stephen Smalley
2020-05-14 14:45 ` Stephen Smalley
2020-05-13 23:16 ` David Howells
2020-05-13 23:25 ` David Howells
2020-05-14 11:00 ` Jarkko Sakkinen
2020-05-14 16:58 ` [PATCH] keys: Move permissions checking decisions into the checking code David Howells
2020-05-14 17:06 ` Casey Schaufler
2020-05-15 15:06 ` Stephen Smalley
2020-05-15 16:45 ` David Howells
2020-05-15 18:55 ` Stephen Smalley
2020-05-15 19:10 ` Casey Schaufler
2020-05-15 22:27 ` David Howells
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