[PATCH 4.20 42/80] selftests/seccomp: Enhance per-arch ptrace syscall skip tests

Greg Kroah-Hartman
2019-02-04T10:52:14Z

From: Kees Cook <keescook@chromium.org>

commit ed5f13261cb65b02c611ae9971677f33581d4286 upstream.

Passing EPERM during syscall skipping was confusing since the test wasn't
actually exercising the errno evaluation -- it was just passing a literal
"1" (EPERM). Instead, expand the tests to check both direct value returns
(positive, 45000 in this case), and errno values (negative, -ESRCH in this
case) to check both fake success and fake failure during syscall skipping.

Reported-by: Colin Ian King <colin.king@canonical.com>
Fixes: a33b2d0359a0 ("selftests/seccomp: Add tests for basic ptrace actions")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <shuah@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/testing/selftests/seccomp/seccomp_bpf.c | 72 ++++++++++++++++++++------
1 file changed, 57 insertions(+), 15 deletions(-)

--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1563,7 +1563,16 @@ TEST_F(TRACE_poke, getpid_runs_normally)
#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)
+# define EXPECT_SYSCALL_RETURN(val, action) \
+ do { \
+ errno = 0; \
+ if (val < 0) { \
+ EXPECT_EQ(-1, action); \
+ EXPECT_EQ(-(val), errno); \
+ } else { \
+ EXPECT_EQ(val, action); \
+ } \
+ } while (0)
#endif

/* Use PTRACE_GETREGS and PTRACE_SETREGS when available. This is useful for
@@ -1602,7 +1611,7 @@ int get_syscall(struct __test_metadata *

/* Architecture-specific syscall changing routine. */
void change_syscall(struct __test_metadata *_metadata,
- pid_t tracee, int syscall)
+ pid_t tracee, int syscall, int result)
{
int ret;
ARCH_REGS regs;
@@ -1661,7 +1670,7 @@ void change_syscall(struct __test_metada
#ifdef SYSCALL_NUM_RET_SHARE_REG
TH_LOG("Can't modify syscall return on this architecture");
#else
- regs.SYSCALL_RET = EPERM;
+ regs.SYSCALL_RET = result;
#endif

#ifdef HAVE_GETREGS
@@ -1689,14 +1698,19 @@ void tracer_syscall(struct __test_metada
case 0x1002:
/* change getpid to getppid. */
EXPECT_EQ(__NR_getpid, get_syscall(_metadata, tracee));
- change_syscall(_metadata, tracee, __NR_getppid);
+ change_syscall(_metadata, tracee, __NR_getppid, 0);
break;
case 0x1003:
- /* skip gettid. */
+ /* skip gettid with valid return code. */
EXPECT_EQ(__NR_gettid, get_syscall(_metadata, tracee));
- change_syscall(_metadata, tracee, -1);
+ change_syscall(_metadata, tracee, -1, 45000);
break;
case 0x1004:
+ /* skip openat with error. */
+ EXPECT_EQ(__NR_openat, get_syscall(_metadata, tracee));
+ change_syscall(_metadata, tracee, -1, -ESRCH);
+ break;
+ case 0x1005:
/* do nothing (allow getppid) */
EXPECT_EQ(__NR_getppid, get_syscall(_metadata, tracee));
break;
@@ -1729,9 +1743,11 @@ void tracer_ptrace(struct __test_metadat
nr = get_syscall(_metadata, tracee);

if (nr == __NR_getpid)
- change_syscall(_metadata, tracee, __NR_getppid);
+ change_syscall(_metadata, tracee, __NR_getppid, 0);
+ if (nr == __NR_gettid)
+ change_syscall(_metadata, tracee, -1, 45000);
if (nr == __NR_openat)
- change_syscall(_metadata, tracee, -1);
+ change_syscall(_metadata, tracee, -1, -ESRCH);
}

FIXTURE_DATA(TRACE_syscall) {
@@ -1748,8 +1764,10 @@ FIXTURE_SETUP(TRACE_syscall)
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1002),
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_gettid, 0, 1),
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1003),
- BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_getppid, 0, 1),
+ BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_openat, 0, 1),
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1004),
+ BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_getppid, 0, 1),
+ BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1005),
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
};

@@ -1797,15 +1815,26 @@ TEST_F(TRACE_syscall, ptrace_syscall_red
EXPECT_NE(self->mypid, syscall(__NR_getpid));
}

-TEST_F(TRACE_syscall, ptrace_syscall_dropped)
+TEST_F(TRACE_syscall, ptrace_syscall_errno)
+{
+ /* 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 ESRCH. */
+ EXPECT_SYSCALL_RETURN(-ESRCH, syscall(__NR_openat));
+}
+
+TEST_F(TRACE_syscall, ptrace_syscall_faked)
{
/* 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_openat));
+ /* Tracer should skip the gettid syscall, resulting fake pid. */
+ EXPECT_SYSCALL_RETURN(45000, syscall(__NR_gettid));
}

TEST_F(TRACE_syscall, syscall_allowed)
@@ -1838,7 +1867,21 @@ TEST_F(TRACE_syscall, syscall_redirected
EXPECT_NE(self->mypid, syscall(__NR_getpid));
}

-TEST_F(TRACE_syscall, syscall_dropped)
+TEST_F(TRACE_syscall, syscall_errno)
+{
+ long ret;
+
+ ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+ ASSERT_EQ(0, ret);
+
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &self->prog, 0, 0);
+ ASSERT_EQ(0, ret);
+
+ /* openat has been skipped and an errno return. */
+ EXPECT_SYSCALL_RETURN(-ESRCH, syscall(__NR_openat));
+}
+
+TEST_F(TRACE_syscall, syscall_faked)
{
long ret;

@@ -1849,8 +1892,7 @@ TEST_F(TRACE_syscall, syscall_dropped)
ASSERT_EQ(0, ret);

/* gettid has been skipped and an altered return value stored. */
- EXPECT_SYSCALL_RETURN(EPERM, syscall(__NR_gettid));
- EXPECT_NE(self->mytid, syscall(__NR_gettid));
+ EXPECT_SYSCALL_RETURN(45000, syscall(__NR_gettid));
}

TEST_F(TRACE_syscall, skip_after_RET_TRACE)