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Subject[PATCH] selftests/seccomp: Add tests for basic ptrace actions
This adds tests for using only ptrace to perform syscall changes, just
to validate matching behavior between seccomp events and ptrace events.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
I'd like this to go through the seccomp tree, since it's part of a number
of other improvements. If I can get an Ack, that would be great. :) Thanks!
---
tools/testing/selftests/seccomp/seccomp_bpf.c | 41 ++++++++++++++++++++++-----
1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 73f5ea6778ce..e61b963f011b 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1262,6 +1262,13 @@ TEST_F(TRACE_poke, getpid_runs_normally)
# error "Do not know how to find your architecture's registers and syscalls"
#endif

+/* When the syscall return can't be changed, stub out the tests for it. */
+#ifdef SYSCALL_NUM_RET_SHARE_REG
+# define EXPECT_SYSCALL_RETURN(val, action) EXPECT_EQ(-1, action)
+#else
+# define EXPECT_SYSCALL_RETURN(val, action) EXPECT_EQ(val, action)
+#endif
+
/* Use PTRACE_GETREGS and PTRACE_SETREGS when available. This is useful for
* architectures without HAVE_ARCH_TRACEHOOK (e.g. User-mode Linux).
*/
@@ -1357,7 +1364,7 @@ void change_syscall(struct __test_metadata *_metadata,
#ifdef SYSCALL_NUM_RET_SHARE_REG
TH_LOG("Can't modify syscall return on this architecture");
#else
- regs.SYSCALL_RET = 1;
+ regs.SYSCALL_RET = EPERM;
#endif

#ifdef HAVE_GETREGS
@@ -1426,6 +1433,8 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee,

if (nr == __NR_getpid)
change_syscall(_metadata, tracee, __NR_getppid);
+ if (nr == __NR_open)
+ change_syscall(_metadata, tracee, -1);
}

FIXTURE_DATA(TRACE_syscall) {
@@ -1480,6 +1489,28 @@ FIXTURE_TEARDOWN(TRACE_syscall)
free(self->prog.filter);
}

+TEST_F(TRACE_syscall, ptrace_syscall_redirected)
+{
+ /* Swap SECCOMP_RET_TRACE tracer for PTRACE_SYSCALL tracer. */
+ teardown_trace_fixture(_metadata, self->tracer);
+ self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, NULL,
+ true);
+
+ /* Tracer will redirect getpid to getppid. */
+ EXPECT_NE(self->mypid, syscall(__NR_getpid));
+}
+
+TEST_F(TRACE_syscall, ptrace_syscall_dropped)
+{
+ /* Swap SECCOMP_RET_TRACE tracer for PTRACE_SYSCALL tracer. */
+ teardown_trace_fixture(_metadata, self->tracer);
+ self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, NULL,
+ true);
+
+ /* Tracer should skip the open syscall, resulting in EPERM. */
+ EXPECT_SYSCALL_RETURN(EPERM, syscall(__NR_open));
+}
+
TEST_F(TRACE_syscall, syscall_allowed)
{
long ret;
@@ -1520,13 +1551,8 @@ TEST_F(TRACE_syscall, syscall_dropped)
ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &self->prog, 0, 0);
ASSERT_EQ(0, ret);

-#ifdef SYSCALL_NUM_RET_SHARE_REG
- /* gettid has been skipped */
- EXPECT_EQ(-1, syscall(__NR_gettid));
-#else
/* gettid has been skipped and an altered return value stored. */
- EXPECT_EQ(1, syscall(__NR_gettid));
-#endif
+ EXPECT_SYSCALL_RETURN(EPERM, syscall(__NR_gettid));
EXPECT_NE(self->mytid, syscall(__NR_gettid));
}

@@ -1557,6 +1583,7 @@ TEST_F(TRACE_syscall, skip_after_RET_TRACE)
ASSERT_EQ(0, ret);

/* Tracer will redirect getpid to getppid, and we should see EPERM. */
+ errno = 0;
EXPECT_EQ(-1, syscall(__NR_getpid));
EXPECT_EQ(EPERM, errno);
}
--
2.7.4

--
Kees Cook
Pixel Security

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