From 1f8266ff58840d698a1e96d2274189de1bdf7969 Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@google.com>
Date: Thu Sep 13 18:12:09 2018 +0200
Subject: [PATCH] apparmor: don't try to replace stale label in ptrace access check
Git-commit: 1f8266ff58840d698a1e96d2274189de1bdf7969
References: git-fixes
Patch-mainline: v4.20-rc1
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@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
security/apparmor/include/context.h | 2 ++
security/apparmor/lsm.c | 4 ++--
2 files changed, 4 insertions(+), 2 deletions(-)
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -108,13 +108,13 @@ static int apparmor_ptrace_access_check(
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;
}
--- a/security/apparmor/include/context.h
+++ b/security/apparmor/include/context.h
@@ -191,6 +191,8 @@ static inline struct aa_label *begin_cur
{
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)