apparmor: add the ability to mediate signals

Add signal mediation where the signal can be mediated based on the
signal, direction, or the label or the peer/target. The signal perms
are verified on a cross check to ensure policy consistency in the case
of incremental policy load/replacement.

The optimization of skipping the cross check when policy is guaranteed
to be consistent (single compile unit) remains to be done.

policy rules have the form of
  SIGNAL_RULE = [ QUALIFIERS ] 'signal' [ SIGNAL ACCESS PERMISSIONS ]
                [ SIGNAL SET ] [ SIGNAL PEER ]

  SIGNAL ACCESS PERMISSIONS = SIGNAL ACCESS | SIGNAL ACCESS LIST

  SIGNAL ACCESS LIST = '(' Comma or space separated list of SIGNAL
                           ACCESS ')'

  SIGNAL ACCESS = ( 'r' | 'w' | 'rw' | 'read' | 'write' | 'send' |
                    'receive' )

  SIGNAL SET = 'set' '=' '(' SIGNAL LIST ')'

  SIGNAL LIST = Comma or space separated list of SIGNALS

  SIGNALS = ( 'hup' | 'int' | 'quit' | 'ill' | 'trap' | 'abrt' |
              'bus' | 'fpe' | 'kill' | 'usr1' | 'segv' | 'usr2' |
	      'pipe' | 'alrm' | 'term' | 'stkflt' | 'chld' | 'cont' |
	      'stop' | 'stp' | 'ttin' | 'ttou' | 'urg' | 'xcpu' |
	      'xfsz' | 'vtalrm' | 'prof' | 'winch' | 'io' | 'pwr' |
	      'sys' | 'emt' | 'exists' | 'rtmin+0' ... 'rtmin+32'
            )

  SIGNAL PEER = 'peer' '=' AARE

eg.
  signal,                                 # allow all signals
  signal send set=(hup, kill) peer=foo,

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 867bcd154c7e..af22f3dfbcce 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -656,6 +656,26 @@ static int apparmor_task_setrlimit(struct task_struct *task,
 	return error;
 }
 
+static int apparmor_task_kill(struct task_struct *target, struct siginfo *info,
+			      int sig, u32 secid)
+{
+	struct aa_label *cl, *tl;
+	int error;
+
+	if (secid)
+		/* TODO: after secid to label mapping is done.
+		 *  Dealing with USB IO specific behavior
+		 */
+		return 0;
+	cl = __begin_current_label_crit_section();
+	tl = aa_get_task_label(target);
+	error = aa_may_signal(cl, tl, sig);
+	aa_put_label(tl);
+	__end_current_label_crit_section(cl);
+
+	return error;
+}
+
 static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_access_check, apparmor_ptrace_access_check),
 	LSM_HOOK_INIT(ptrace_traceme, apparmor_ptrace_traceme),
@@ -697,6 +717,7 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bprm_secureexec, apparmor_bprm_secureexec),
 
 	LSM_HOOK_INIT(task_setrlimit, apparmor_task_setrlimit),
+	LSM_HOOK_INIT(task_kill, apparmor_task_kill),
 };
 
 /*