From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D825AC33CB3 for ; Wed, 15 Jan 2020 18:38:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDB352467A for ; Wed, 15 Jan 2020 18:38:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729140AbgAOSis (ORCPT ); Wed, 15 Jan 2020 13:38:48 -0500 Received: from mail.hallyn.com ([178.63.66.53]:56086 "EHLO mail.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729028AbgAOSir (ORCPT ); Wed, 15 Jan 2020 13:38:47 -0500 Received: by mail.hallyn.com (Postfix, from userid 1001) id AB27D101E; Wed, 15 Jan 2020 12:38:45 -0600 (CST) Date: Wed, 15 Jan 2020 12:38:45 -0600 From: "Serge E. Hallyn" To: Christian Brauner Cc: eparis@redhat.com, jannh@google.com, linux-kernel@vger.kernel.org, oleg@redhat.com, shallyn@cisco.com, stable@vger.kernel.org Subject: Re: [PATCH v2] ptrace: reintroduce usage of subjective credentials in ptrace_has_cap() Message-ID: <20200115183845.GA25149@mail.hallyn.com> References: <20200115171736.16994-1-christian.brauner@ubuntu.com> <20200115172355.19209-1-christian.brauner@ubuntu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200115172355.19209-1-christian.brauner@ubuntu.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 15, 2020 at 06:23:55PM +0100, Christian Brauner wrote: > Commit 69f594a38967 ("ptrace: do not audit capability check when outputing /proc/pid/stat") > introduced the ability to opt out of audit messages for accesses to > various proc files since they are not violations of policy. > While doing so it somehow switched the check from ns_capable() to > has_ns_capability{_noaudit}(). That means it switched from checking the > subjective credentials of the task to using the objective credentials. I > couldn't find the original lkml thread and so I don't know why this switch > was done. But it seems wrong since ptrace_has_cap() is currently only used > in ptrace_may_access(). And it's used to check whether the calling task > (subject) has the CAP_SYS_PTRACE capability in the provided user namespace > to operate on the target task (object). According to the cred.h comments > this would mean the subjective credentials of the calling task need to be > used. > This switches it to use security_capable() because we only call > ptrace_has_cap() in ptrace_may_access() and in there we already have a > stable reference to the calling tasks creds under cred_guard_mutex so > there's no need to go through another series of dereferences and rcu > locking done in ns_capable{_noaudit}(). > > Cc: Serge Hallyn Thanks. Reviewed-by: Serge Hallyn > Cc: Jann Horn > Cc: Oleg Nesterov > Cc: Eric Paris > Cc: stable@vger.kernel.org > Fixes: 69f594a38967 ("ptrace: do not audit capability check when outputing /proc/pid/stat") > Signed-off-by: Christian Brauner > --- > kernel/ptrace.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/kernel/ptrace.c b/kernel/ptrace.c > index cb9ddcc08119..d146133e97f1 100644 > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -264,12 +264,13 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state) > return ret; > } > > -static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode) > +static int ptrace_has_cap(const struct cred *cred, struct user_namespace *ns, > + unsigned int mode) > { > if (mode & PTRACE_MODE_NOAUDIT) > - return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE); > + return security_capable(cred, ns, CAP_SYS_PTRACE, CAP_OPT_NOAUDIT); > else > - return has_ns_capability(current, ns, CAP_SYS_PTRACE); > + return security_capable(cred, ns, CAP_SYS_PTRACE, CAP_OPT_NONE); > } > > /* Returns 0 on success, -errno on denial. */ > @@ -321,7 +322,7 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) > gid_eq(caller_gid, tcred->sgid) && > gid_eq(caller_gid, tcred->gid)) > goto ok; > - if (ptrace_has_cap(tcred->user_ns, mode)) > + if (ptrace_has_cap(cred, tcred->user_ns, mode)) > goto ok; > rcu_read_unlock(); > return -EPERM; > @@ -340,7 +341,7 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) > mm = task->mm; > if (mm && > ((get_dumpable(mm) != SUID_DUMP_USER) && > - !ptrace_has_cap(mm->user_ns, mode))) > + !ptrace_has_cap(cred, mm->user_ns, mode))) > return -EPERM; > > return security_ptrace_access_check(task, mode); > > base-commit: b3a987b0264d3ddbb24293ebff10eddfc472f653 > -- > 2.25.0