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apparmor: don't try to replace stale label in ptrace access check

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[ 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@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jann Horn 2018-09-13 18:12:09 +02:00 committed by Greg Kroah-Hartman
parent 961e9f394d
commit 49f3e22df7
2 changed files with 4 additions and 2 deletions
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2
security/apparmor/include/context.h
View File

@ -191,6 +191,8 @@ 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)

4
security/apparmor/lsm.c
View File

@ -108,12 +108,12 @@ 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;
}