diff mbox

[05/14] seccomp: recheck the syscall after RET_TRACE

Message ID 1465506124-21866-6-git-send-email-keescook@chromium.org (mailing list archive)
State Not Applicable
Headers show

Commit Message

Kees Cook June 9, 2016, 9:01 p.m. UTC 
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: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
---
 kernel/seccomp.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

Comments

Andy Lutomirski June 9, 2016, 10:46 p.m. UTC | #1 
On Thu, Jun 9, 2016 at 2:01 PM, Kees Cook <keescook@chromium.org> wrote:
> 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: Kees Cook <keescook@chromium.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> ---
>  kernel/seccomp.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 14a37d71b612..54d15eb2b701 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -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)

This patch looks good with one minor nit: I read this as "pass true if
you want to recheck after trace", which is exactly the opposite of how
it works.

--Andy
diff mbox

Patch

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 14a37d71b612..54d15eb2b701 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -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 @@  skip:
 	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();
 	}