linux-kernel - [PATCH AUTOSEL 4.19 009/671] apparmor: don't try to replace stale label in ptrace access check

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Message-Id: <20200116165502.8838-9-sashal@kernel.org>
Date:   Thu, 16 Jan 2020 11:44:00 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jann Horn <jannh@...gle.com>,
        John Johansen <john.johansen@...onical.com>,
        Sasha Levin <sashal@...nel.org>,
        linux-security-module@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 009/671] apparmor: don't try to replace stale label in ptrace access check

From: Jann Horn <jannh@...gle.com>

[ Upstream commit 1f8266ff58840d698a1e96d2274189de1bdf7969 ]

As a comment above begin_current_label_crit_section() explains,
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 ptrace access check (which runs with a task lock held)
violated this rule.

Also add a might_sleep() assertion to begin_current_label_crit_section(),
because asserts are less likely to be ignored than comments.

Fixes: b2d09ae449ced ("apparmor: move ptrace checks to using labels")
Signed-off-by: Jann Horn <jannh@...gle.com>
Signed-off-by: John Johansen <john.johansen@...onical.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 security/apparmor/include/cred.h | 2 ++
 security/apparmor/lsm.c          | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/apparmor/include/cred.h b/security/apparmor/include/cred.h
index e287b7d0d4be..265ae6641a06 100644
--- a/security/apparmor/include/cred.h
+++ b/security/apparmor/include/cred.h
@@ -151,6 +151,8 @@ static inline struct aa_label *begin_current_label_crit_section(void)
 {
 	struct aa_label *label = aa_current_raw_label();
 
+	might_sleep();
+
 	if (label_is_stale(label)) {
 		label = aa_get_newest_label(label);
 		if (aa_replace_current_label(label) == 0)
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 8b8b70620bbe..e3f40c20b9b4 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -114,13 +114,13 @@ static int apparmor_ptrace_access_check(struct task_struct *child,
 	struct aa_label *tracer, *tracee;
 	int error;
 
-	tracer = begin_current_label_crit_section();
+	tracer = __begin_current_label_crit_section();
 	tracee = aa_get_task_label(child);
 	error = aa_may_ptrace(tracer, tracee,
 			(mode & PTRACE_MODE_READ) ? AA_PTRACE_READ
 						  : AA_PTRACE_TRACE);
 	aa_put_label(tracee);
-	end_current_label_crit_section(tracer);
+	__end_current_label_crit_section(tracer);
 
 	return error;
 }
-- 
2.20.1