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Date: Fri, 25 Jan 2019 12:11:54 -0700
From: shuah <shuah@...nel.org>
To: Kees Cook <keescook@...omium.org>,
Colin Ian King <colin.king@...onical.com>
Cc: Andy Lutomirski <luto@...capital.net>,
Will Drewry <wad@...omium.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>, kernel-janitors@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>, shuah <shuah@...nel.org>
Subject: Re: [PATCH] selftests/seccomp: Enhance per-arch ptrace syscall skip
tests
On 1/25/19 11:46 AM, Kees Cook wrote:
> On Sat, Jan 26, 2019 at 7:42 AM Colin Ian King <colin.king@...onical.com> wrote:
>>
>> On 25/01/2019 18:33, Kees Cook wrote:
>>> 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@...onical.com>
>>> Fixes: a33b2d0359a0 ("selftests/seccomp: Add tests for basic ptrace actions")
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Kees Cook <keescook@...omium.org>
>>> ---
>>> Colin, does this end up working on s390? Based on your bug report, I
>>> suspect the positive value tests will fail, but the errno tests will
>>> pass. If that's true, I think something is wrong in the s390 handling.
>>> (And it may just be that the ptrace code to rewrite syscalls on s390
>>> in the test is wrong...) But splitting these tests up should tell us more.
>>> ---
>>> tools/testing/selftests/seccomp/seccomp_bpf.c | 72 +++++++++++++++----
>>> 1 file changed, 57 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
>>> index 496a9a8c773a..7e632b465ab4 100644
>>> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
>>> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
>>> @@ -1608,7 +1608,16 @@ 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
>>> @@ -1647,7 +1656,7 @@ int get_syscall(struct __test_metadata *_metadata, pid_t tracee)
>>>
>>> /* 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;
>>> @@ -1706,7 +1715,7 @@ 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 = EPERM;
>>> + regs.SYSCALL_RET = result;
>>> #endif
>>>
>>> #ifdef HAVE_GETREGS
>>> @@ -1734,14 +1743,19 @@ void tracer_syscall(struct __test_metadata *_metadata, pid_t tracee,
>>> 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;
>>> @@ -1774,9 +1788,11 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee,
>>> 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) {
>>> @@ -1793,8 +1809,10 @@ 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),
>>> };
>>>
>>> @@ -1842,15 +1860,26 @@ TEST_F(TRACE_syscall, ptrace_syscall_redirected)
>>> 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)
>>> @@ -1883,7 +1912,21 @@ 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;
>>>
>>> @@ -1894,8 +1937,7 @@ 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)
>>>
>> Works perfectly. Thanks Kees.
>>
>> Tested-by: Colin Ian King <colin.king@...onical.com>
>
> Oh excellent! Thanks. :) Shuah can you queue this up?
>
Yup will do - I am planning to apply bunch of fixes this afternoon.
Hoping to get them into rc5
thanks,
-- Shuah
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