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

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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: b2d09ae449 ("apparmor: move ptrace checks to using labels")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
This commit is contained in:
Jann Horn 2018-09-13 18:12:09 +02:00 • committed by John Johansen
parent 5f997580e8
commit 1f8266ff58
2 changed files with 4 additions and 2 deletions
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4
security/apparmor/lsm.c
View file

@ -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;
}