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Commit ce6526e8 authored by Kees Cook's avatar Kees Cook
Browse files

seccomp: recheck the syscall after RET_TRACE 



When RET_TRACE triggers, a tracer may change a syscall into something that
should be filtered by seccomp. This re-runs seccomp after a trace event
to make sure things continue to pass.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
parent 8112c4f1

kernel/seccomp.c

+18 −3
Original line number Diff line number Diff line
@@ -556,7 +556,8 @@ void secure_computing_strict(int this_syscall) 
#else



#ifdef CONFIG_SECCOMP_FILTER

static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)

static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,

			    const bool recheck_after_trace)

{

	u32 filter_ret, action;

	int data;
@@ -588,6 +589,10 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd) 
		goto skip;



	case SECCOMP_RET_TRACE:

		/* We've been put in this state by the ptracer already. */

		if (recheck_after_trace)

			return 0;



		/* ENOSYS these calls if there is no tracer attached. */

		if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {

			syscall_set_return_value(current,
@@ -611,6 +616,15 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd) 
		if (this_syscall < 0)

			goto skip;



		/*

		 * Recheck the syscall, since it may have changed. This

		 * intentionally uses a NULL struct seccomp_data to force

		 * a reload of all registers. This does not goto skip since

		 * a skip would have already been reported.

		 */

		if (__seccomp_filter(this_syscall, NULL, true))

			return -1;



		return 0;



	case SECCOMP_RET_ALLOW:
@@ -629,7 +643,8 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd) 
	return -1;

}

#else

static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)

static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,

			    const bool recheck_after_trace)

{

	BUG();

}
@@ -652,7 +667,7 @@ int __secure_computing(const struct seccomp_data *sd) 
		__secure_computing_strict(this_syscall);  /* may call do_exit */

		return 0;

	case SECCOMP_MODE_FILTER:

		return __seccomp_filter(this_syscall, sd);

		return __seccomp_filter(this_syscall, sd, false);

	default:

		BUG();

	}