lkml.org 
[lkml]   [2018]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v5 3/5] SELinux: Prepare for PTRACE_MODE_SCHED
From
Date
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@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);
>

\
 
 \ /
  Last update: 2018-09-27 17:49    [W:0.107 / U:0.572 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site