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 <keesc...@chromium.org>
Cc: Andy Lutomirski <l...@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)
{
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();
}
--
2.7.4
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