From: sds@tycho.nsa.gov (Stephen Smalley)
To: linux-security-module@vger.kernel.org
Subject: [PATCH v5 3/5] SELinux: Prepare for PTRACE_MODE_SCHED
Date: Thu, 27 Sep 2018 11:50:07 -0400 [thread overview]
Message-ID: <6e21f471-ff88-c57c-8892-e0bb626bea12@tycho.nsa.gov> (raw)
In-Reply-To: <20180926203446.2004-4-casey.schaufler@intel.com>
On 09/26/2018 04:34 PM, Casey Schaufler wrote:
> From: Casey Schaufler <casey@schaufler-ca.com>
>
> A ptrace access check with mode PTRACE_MODE_SCHED gets called
> from process switching code. This precludes the use of audit or avc,
> as the locking is incompatible. The only available check that
> can be made without using avc is a comparison of the secids.
> This is not very satisfactory as it will indicate possible
> vulnerabilies much too aggressively.
Can you document (in the patch description and/or in the inline
documentation in lsm_hooks.h) what locks can be safely used when this
hook is called with PTRACE_MODE_SCHED? rcu_read_lock() seemingly must
be safe since it is being called by task_sid() below. Are any other
locking primitives safe?
Does the PTRACE_MODE_SCHED check have to occur while holding the
scheduler lock, or could it be performed before taking the lock?
Can you cite the commit or patch posting (e.g. from lore or patchwork)
that defines PTRACE_MODE_SCHED and its usage as part of the patch
description for context? Is this based on the v7 patchset, e.g.
https://lore.kernel.org/lkml/nycvar.YFH.7.76.1809251437340.15880 at cbobk.fhfr.pm/
>
> Signed-off-by: Casey Schaufler <casey.schaufler@intel.com>
> ---
> security/selinux/hooks.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index ad9a9b8e9979..160239791007 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2267,6 +2267,8 @@ static int selinux_ptrace_access_check(struct task_struct *child,
> u32 sid = current_sid();
> u32 csid = task_sid(child);
>
> + if (mode & PTRACE_MODE_SCHED)
> + return sid == csid ? 0 : -EACCES;
IIUC, this logic is essentially the same as the uid-based check,
including the fact that even a "privileged" process is not given any
special handling since they always return false from ptrace_has_cap()
for PTRACE_MODE_SCHED. If they are ok with applying IBPB whenever uids
differ, then doing so whenever sids/contexts differ does not seem like
an onerous thing.
> if (mode & PTRACE_MODE_READ)
> return avc_has_perm(&selinux_state,
> sid, csid, SECCLASS_FILE, FILE__READ, NULL);
>
next prev parent reply other threads:[~2018-09-27 15:50 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-26 20:34 [PATCH v5 0/5] LSM: Support ptrace sidechannel access checks Casey Schaufler
2018-09-26 20:34 ` [PATCH v5 1/5] AppArmor: Prepare for PTRACE_MODE_SCHED Casey Schaufler
2018-09-26 21:16 ` Jann Horn
2018-09-26 21:18 ` Jann Horn
2018-09-26 22:47 ` Schaufler, Casey
2018-09-26 20:34 ` [PATCH v5 2/5] Smack: " Casey Schaufler
2018-09-26 21:30 ` Jann Horn
2018-09-26 22:53 ` Schaufler, Casey
2018-09-26 22:58 ` Jann Horn
2018-10-04 7:47 ` Jiri Kosina
2018-10-04 11:36 ` Jann Horn
2018-10-16 11:44 ` Jiri Kosina
2018-09-26 20:34 ` [PATCH v5 3/5] SELinux: " Casey Schaufler
2018-09-27 15:50 ` Stephen Smalley [this message]
2018-09-27 16:23 ` Schaufler, Casey
2018-09-26 20:34 ` [PATCH v5 4/5] Capability: Complete PTRACE_MODE_SCHED Casey Schaufler
2018-09-26 21:26 ` Jann Horn
2018-09-26 22:24 ` Schaufler, Casey
2018-09-26 20:34 ` [PATCH v5 5/5] sidechannel: Linux Security Module for sidechannel Casey Schaufler
2018-09-27 21:45 ` James Morris
2018-09-27 22:39 ` Casey Schaufler
2018-09-27 22:47 ` James Morris
2018-09-27 23:19 ` Schaufler, Casey
2018-09-27 23:43 ` James Morris
2018-09-27 23:47 ` Jann Horn
2018-09-28 16:33 ` James Morris
2018-09-28 17:40 ` Schaufler, Casey
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=6e21f471-ff88-c57c-8892-e0bb626bea12@tycho.nsa.gov \
--to=sds@tycho.nsa.gov \
--cc=linux-security-module@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).