linux-kernel - [PATCH] apparmor: don't try to replace stale label in ptraceme check

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Message-Id: <20180929014926.227002-1-jannh@google.com>
Date:   Sat, 29 Sep 2018 03:49:26 +0200
From:   Jann Horn <jannh@...gle.com>
To:     John Johansen <john.johansen@...onical.com>,
        apparmor@...ts.ubuntu.com, jannh@...gle.com
Cc:     linux-kernel@...r.kernel.org, Cyrill Gorcunov <gorcunov@...il.com>,
        kernel test robot <rong.a.chen@...el.com>
Subject: [PATCH] apparmor: don't try to replace stale label in ptraceme check

begin_current_label_crit_section() must run in sleepable context because
when label_is_stale() is true, aa_replace_current_label() runs, which uses
prepare_creds(), which can sleep.

Until now, the ptraceme access check (which runs with tasklist_lock held)
violated this rule.

Fixes: b2d09ae449ced ("apparmor: move ptrace checks to using labels")
Reported-by: Cyrill Gorcunov <gorcunov@...il.com>
Reported-by: kernel test robot <rong.a.chen@...el.com>
Signed-off-by: Jann Horn <jannh@...gle.com>
---
 security/apparmor/lsm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 8c7f46a6a8dc..0f56431b4b2f 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -131,11 +131,11 @@ static int apparmor_ptrace_traceme(struct task_struct *parent)
 	struct aa_label *tracer, *tracee;
 	int error;
 
-	tracee = begin_current_label_crit_section();
+	tracee = __begin_current_label_crit_section();
 	tracer = aa_get_task_label(parent);
 	error = aa_may_ptrace(tracer, tracee, AA_PTRACE_TRACE);
 	aa_put_label(tracer);
-	end_current_label_crit_section(tracee);
+	__end_current_label_crit_section(tracee);
 
 	return error;
 }
-- 
2.19.0.605.g01d371f741-goog