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Message-Id: <1502426037-3777-5-git-send-email-tyhicks@canonical.com>
Date: Fri, 11 Aug 2017 04:33:55 +0000
From: Tyler Hicks <tyhicks@...onical.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andy Lutomirski <luto@...capital.net>,
Will Drewry <wad@...omium.org>,
Paul Moore <paul@...l-moore.com>,
Eric Paris <eparis@...hat.com>,
John Crispin <john@...ozen.org>,
Tycho Andersen <tycho@...ker.com>, linux-audit@...hat.com,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: [PATCH v6 4/6] seccomp: Selftest for detection of filter flag support
Userspace needs to be able to reliably detect the support of a filter
flag. A good way of doing that is by attempting to enter filter mode,
with the flag bit(s) in question set, and a NULL pointer for the args
parameter of seccomp(2). EFAULT indicates that the flag is valid and
EINVAL indicates that the flag is invalid.
This patch adds a selftest that can be used to test this method of
detection in userspace.
Signed-off-by: Tyler Hicks <tyhicks@...onical.com>
---
tools/testing/selftests/seccomp/seccomp_bpf.c | 59 +++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index d3a78ec..ed4528c 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1918,6 +1918,65 @@ TEST(seccomp_syscall_mode_lock)
}
}
+/* Test detection of known and unknown filter flags. Userspace needs to be able
+ * to check if a filter flag is supported by the current kernel and a good way
+ * of doing that is by attempting to enter filter mode, with the flag bit in
+ * question set, and a NULL pointer for the _args_ parameter. EFAULT indicates
+ * that the flag is valid and EINVAL indicates that the flag is invalid.
+ */
+TEST(detect_seccomp_filter_flags)
+{
+ unsigned int flags[] = { SECCOMP_FILTER_FLAG_TSYNC,
+ SECCOMP_FILTER_FLAG_KILL_PROCESS };
+ unsigned int flag, all_flags;
+ int i;
+ long ret;
+
+ /* Test detection of known-good filter flags */
+ for (i = 0, all_flags = 0; i < ARRAY_SIZE(flags); i++) {
+ flag = flags[i];
+ ret = seccomp(SECCOMP_SET_MODE_FILTER, flag, NULL);
+ ASSERT_NE(ENOSYS, errno) {
+ TH_LOG("Kernel does not support seccomp syscall!");
+ }
+ EXPECT_EQ(-1, ret);
+ EXPECT_EQ(EFAULT, errno) {
+ TH_LOG("Failed to detect that a known-good filter flag (0x%X) is supported!",
+ flag);
+ }
+
+ all_flags |= flag;
+ }
+
+ /* Test detection of all known-good filter flags */
+ ret = seccomp(SECCOMP_SET_MODE_FILTER, all_flags, NULL);
+ EXPECT_EQ(-1, ret);
+ EXPECT_EQ(EFAULT, errno) {
+ TH_LOG("Failed to detect that all known-good filter flags (0x%X) are supported!",
+ all_flags);
+ }
+
+ /* Test detection of an unknown filter flag */
+ flag = -1;
+ ret = seccomp(SECCOMP_SET_MODE_FILTER, flag, NULL);
+ EXPECT_EQ(-1, ret);
+ EXPECT_EQ(EINVAL, errno) {
+ TH_LOG("Failed to detect that an unknown filter flag (0x%X) is unsupported!",
+ flag);
+ }
+
+ /* Test detection of an unknown filter flag that may simply need to be
+ * added to this test
+ */
+ flag = flags[ARRAY_SIZE(flags) - 1] << 1;
+ ret = seccomp(SECCOMP_SET_MODE_FILTER, flag, NULL);
+ EXPECT_EQ(-1, ret);
+ EXPECT_EQ(EINVAL, errno) {
+ TH_LOG("Failed to detect that an unknown filter flag (0x%X) is unsupported! Does a new flag need to be added to this test?",
+ flag);
+ }
+}
+
TEST(TSYNC_first)
{
struct sock_filter filter[] = {
--
2.7.4
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