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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@canonical.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Tyler Hicks 2017-08-11 04:33:55 +00:00 committed by Kees Cook
parent 0ddec0fc89
commit 2b7ea5b5b5
1 changed files with 60 additions and 0 deletions
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60
tools/testing/selftests/seccomp/seccomp_bpf.c
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@ -1835,6 +1835,66 @@ 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 };
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[] = {