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Subject[PATCH v2 3/4] selftests/seccomp: Refactor RET_ERRNO tests
Date
This refactors the errno tests (since they all use the same pattern for
their filter) and adds a RET_DATA field ordering test.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
---
tools/testing/selftests/seccomp/seccomp_bpf.c | 95 ++++++++++++++++-----------
1 file changed, 58 insertions(+), 37 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 73f5ea6778ce..ee78a53da5d1 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -136,7 +136,7 @@ TEST(no_new_privs_support)
}
}

-/* Tests kernel support by checking for a copy_from_user() fault on * NULL. */
+/* Tests kernel support by checking for a copy_from_user() fault on NULL. */
TEST(mode_filter_support)
{
long ret;
@@ -541,26 +541,30 @@ TEST(arg_out_of_range)
EXPECT_EQ(EINVAL, errno);
}

+#define ERRNO_FILTER(name, errno) \
+ struct sock_filter _read_filter_##name[] = { \
+ BPF_STMT(BPF_LD|BPF_W|BPF_ABS, \
+ offsetof(struct seccomp_data, nr)), \
+ BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_read, 0, 1), \
+ BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ERRNO | errno), \
+ BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW), \
+ }; \
+ struct sock_fprog prog_##name = { \
+ .len = (unsigned short)ARRAY_SIZE(_read_filter_##name), \
+ .filter = _read_filter_##name, \
+ }
+
+/* Make sure basic errno values are correctly passed through a filter. */
TEST(ERRNO_valid)
{
- struct sock_filter filter[] = {
- BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
- offsetof(struct seccomp_data, nr)),
- BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_read, 0, 1),
- BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ERRNO | E2BIG),
- BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
- };
- struct sock_fprog prog = {
- .len = (unsigned short)ARRAY_SIZE(filter),
- .filter = filter,
- };
+ ERRNO_FILTER(valid, E2BIG);
long ret;
pid_t parent = getppid();

ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
ASSERT_EQ(0, ret);

- ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_valid);
ASSERT_EQ(0, ret);

EXPECT_EQ(parent, syscall(__NR_getppid));
@@ -568,26 +572,17 @@ TEST(ERRNO_valid)
EXPECT_EQ(E2BIG, errno);
}

+/* Make sure an errno of zero is correctly handled by the arch code. */
TEST(ERRNO_zero)
{
- struct sock_filter filter[] = {
- BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
- offsetof(struct seccomp_data, nr)),
- BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_read, 0, 1),
- BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ERRNO | 0),
- BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
- };
- struct sock_fprog prog = {
- .len = (unsigned short)ARRAY_SIZE(filter),
- .filter = filter,
- };
+ ERRNO_FILTER(zero, 0);
long ret;
pid_t parent = getppid();

ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
ASSERT_EQ(0, ret);

- ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_zero);
ASSERT_EQ(0, ret);

EXPECT_EQ(parent, syscall(__NR_getppid));
@@ -595,26 +590,21 @@ TEST(ERRNO_zero)
EXPECT_EQ(0, read(0, NULL, 0));
}

+/*
+ * The SECCOMP_RET_DATA mask is 16 bits wide, but errno is smaller.
+ * This tests that the errno value gets capped correctly, fixed by
+ * 580c57f10768 ("seccomp: cap SECCOMP_RET_ERRNO data to MAX_ERRNO").
+ */
TEST(ERRNO_capped)
{
- struct sock_filter filter[] = {
- BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
- offsetof(struct seccomp_data, nr)),
- BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_read, 0, 1),
- BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ERRNO | 4096),
- BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
- };
- struct sock_fprog prog = {
- .len = (unsigned short)ARRAY_SIZE(filter),
- .filter = filter,
- };
+ ERRNO_FILTER(capped, 4096);
long ret;
pid_t parent = getppid();

ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
ASSERT_EQ(0, ret);

- ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_capped);
ASSERT_EQ(0, ret);

EXPECT_EQ(parent, syscall(__NR_getppid));
@@ -622,6 +612,37 @@ TEST(ERRNO_capped)
EXPECT_EQ(4095, errno);
}

+/*
+ * Filters are processed in reverse order: last applied is executed first.
+ * Since only the SECCOMP_RET_ACTION mask is tested for return values, the
+ * SECCOMP_RET_DATA mask results will follow the most recently applied
+ * matching filter return (and not the lowest or highest value).
+ */
+TEST(ERRNO_order)
+{
+ ERRNO_FILTER(first, 11);
+ ERRNO_FILTER(second, 13);
+ ERRNO_FILTER(third, 12);
+ long ret;
+ pid_t parent = getppid();
+
+ ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+ ASSERT_EQ(0, ret);
+
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_first);
+ ASSERT_EQ(0, ret);
+
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_second);
+ ASSERT_EQ(0, ret);
+
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_third);
+ ASSERT_EQ(0, ret);
+
+ EXPECT_EQ(parent, syscall(__NR_getppid));
+ EXPECT_EQ(-1, read(0, NULL, 0));
+ EXPECT_EQ(12, errno);
+}
+
FIXTURE_DATA(TRAP) {
struct sock_fprog prog;
};
--
2.7.4
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