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

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>

diff --git a/security/apparmor/include/cred.h b/security/apparmor/include/cred.h
index e287b7d0d4bebcf2cc83d9add032fdb1feed54c0..265ae6641a0644e84e40c7f774f4f447a1df3fc2 100644 (file)
--- 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 74f17376202bd1cf36cafcf849abd06fe36ec35a..f09fea0b4db7ecf2884df659fccaf52fa58b5c8c 100644 (file)
--- 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;
 }