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Commit 7a0cf094 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

signal: Correct namespace fixups of si_pid and si_uid 



The function send_signal was split from __send_signal so that it would
be possible to bypass the namespace logic based upon current[1].  As it
turns out the si_pid and the si_uid fixup are both inappropriate in
the case of kill_pid_usb_asyncio so move that logic into send_signal.

It is difficult to arrange but possible for a signal with an si_code
of SI_TIMER or SI_SIGIO to be sent across namespace boundaries.  In
which case tests for when it is ok to change si_pid and si_uid based
on SI_FROMUSER are incorrect.  Replace the use of SI_FROMUSER with a
new test has_si_pid_and_used based on siginfo_layout.

Now that the uid fixup is no longer present after expanding
SEND_SIG_NOINFO properly calculate the si_uid that the target
task needs to read.

[1] 7978b567 ("signals: add from_ancestor_ns parameter to send_signal()")
Cc: stable@vger.kernel.org
Fixes: 6588c1e3 ("signals: SI_USER: Masquerade si_pid when crossing pid ns boundary")
Fixes: 6b550f94 ("user namespace: make signal.c respect user namespaces")
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 70f1b0d3

kernel/signal.c

+40 −27
Original line number Diff line number Diff line
@@ -1056,27 +1056,6 @@ static inline bool legacy_queue(struct sigpending *signals, int sig) 
	return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);

}



#ifdef CONFIG_USER_NS

static inline void userns_fixup_signal_uid(struct kernel_siginfo *info, struct task_struct *t)

{

	if (current_user_ns() == task_cred_xxx(t, user_ns))

		return;



	if (SI_FROMKERNEL(info))

		return;



	rcu_read_lock();

	info->si_uid = from_kuid_munged(task_cred_xxx(t, user_ns),

					make_kuid(current_user_ns(), info->si_uid));

	rcu_read_unlock();

}

#else

static inline void userns_fixup_signal_uid(struct kernel_siginfo *info, struct task_struct *t)

{

	return;

}

#endif



static int __send_signal(int sig, struct kernel_siginfo *info, struct task_struct *t,

			enum pid_type type, int from_ancestor_ns)

{
@@ -1134,7 +1113,11 @@ static int __send_signal(int sig, struct kernel_siginfo *info, struct task_struc 
			q->info.si_code = SI_USER;

			q->info.si_pid = task_tgid_nr_ns(current,

							task_active_pid_ns(t));

			q->info.si_uid = from_kuid_munged(current_user_ns(), current_uid());

			rcu_read_lock();

			q->info.si_uid =

				from_kuid_munged(task_cred_xxx(t, user_ns),

						 current_uid());

			rcu_read_unlock();

			break;

		case (unsigned long) SEND_SIG_PRIV:

			clear_siginfo(&q->info);
@@ -1146,13 +1129,8 @@ static int __send_signal(int sig, struct kernel_siginfo *info, struct task_struc 
			break;

		default:

			copy_siginfo(&q->info, info);

			if (from_ancestor_ns)

				q->info.si_pid = 0;

			break;

		}



		userns_fixup_signal_uid(&q->info, t);



	} else if (!is_si_special(info)) {

		if (sig >= SIGRTMIN && info->si_code != SI_USER) {

			/*
@@ -1196,6 +1174,28 @@ static int __send_signal(int sig, struct kernel_siginfo *info, struct task_struc 
	return ret;

}



static inline bool has_si_pid_and_uid(struct kernel_siginfo *info)

{

	bool ret = false;

	switch (siginfo_layout(info->si_signo, info->si_code)) {

	case SIL_KILL:

	case SIL_CHLD:

	case SIL_RT:

		ret = true;

		break;

	case SIL_TIMER:

	case SIL_POLL:

	case SIL_FAULT:

	case SIL_FAULT_MCEERR:

	case SIL_FAULT_BNDERR:

	case SIL_FAULT_PKUERR:

	case SIL_SYS:

		ret = false;

		break;

	}

	return ret;

}



static int send_signal(int sig, struct kernel_siginfo *info, struct task_struct *t,

			enum pid_type type)

{
@@ -1205,7 +1205,20 @@ static int send_signal(int sig, struct kernel_siginfo *info, struct task_struct 
	from_ancestor_ns = si_fromuser(info) &&

			   !task_pid_nr_ns(current, task_active_pid_ns(t));

#endif

	if (!is_si_special(info) && has_si_pid_and_uid(info)) {

		struct user_namespace *t_user_ns;



		rcu_read_lock();

		t_user_ns = task_cred_xxx(t, user_ns);

		if (current_user_ns() != t_user_ns) {

			kuid_t uid = make_kuid(current_user_ns(), info->si_uid);

			info->si_uid = from_kuid_munged(t_user_ns, uid);

		}

		rcu_read_unlock();



		if (!task_pid_nr_ns(current, task_active_pid_ns(t)))

			info->si_pid = 0;

	}

	return __send_signal(sig, info, t, type, from_ancestor_ns);

}