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keesShuah Khan
kees
authored and
Shuah Khan
committedJan 25, 2019
selftests/seccomp: Enhance per-arch ptrace syscall skip tests
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: a33b2d0 ("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>
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‎tools/testing/selftests/seccomp/seccomp_bpf.c‎

Lines changed: 57 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -1608,7 +1608,16 @@ TEST_F(TRACE_poke, getpid_runs_normally)
16081608
#ifdef SYSCALL_NUM_RET_SHARE_REG
16091609
# define EXPECT_SYSCALL_RETURN(val, action) EXPECT_EQ(-1, action)
16101610
#else
1611-
# define EXPECT_SYSCALL_RETURN(val, action) EXPECT_EQ(val, action)
1611+
# define EXPECT_SYSCALL_RETURN(val, action) \
1612+
do { \
1613+
errno = 0; \
1614+
if (val < 0) { \
1615+
EXPECT_EQ(-1, action); \
1616+
EXPECT_EQ(-(val), errno); \
1617+
} else { \
1618+
EXPECT_EQ(val, action); \
1619+
} \
1620+
} while (0)
16121621
#endif
16131622

16141623
/* 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)
16471656

16481657
/* Architecture-specific syscall changing routine. */
16491658
void change_syscall(struct __test_metadata *_metadata,
1650-
pid_t tracee, int syscall)
1659+
pid_t tracee, int syscall, int result)
16511660
{
16521661
int ret;
16531662
ARCH_REGS regs;
@@ -1706,7 +1715,7 @@ void change_syscall(struct __test_metadata *_metadata,
17061715
#ifdef SYSCALL_NUM_RET_SHARE_REG
17071716
TH_LOG("Can't modify syscall return on this architecture");
17081717
#else
1709-
regs.SYSCALL_RET = EPERM;
1718+
regs.SYSCALL_RET = result;
17101719
#endif
17111720

17121721
#ifdef HAVE_GETREGS
@@ -1734,14 +1743,19 @@ void tracer_syscall(struct __test_metadata *_metadata, pid_t tracee,
17341743
case 0x1002:
17351744
/* change getpid to getppid. */
17361745
EXPECT_EQ(__NR_getpid, get_syscall(_metadata, tracee));
1737-
change_syscall(_metadata, tracee, __NR_getppid);
1746+
change_syscall(_metadata, tracee, __NR_getppid, 0);
17381747
break;
17391748
case 0x1003:
1740-
/* skip gettid. */
1749+
/* skip gettid with valid return code. */
17411750
EXPECT_EQ(__NR_gettid, get_syscall(_metadata, tracee));
1742-
change_syscall(_metadata, tracee, -1);
1751+
change_syscall(_metadata, tracee, -1, 45000);
17431752
break;
17441753
case 0x1004:
1754+
/* skip openat with error. */
1755+
EXPECT_EQ(__NR_openat, get_syscall(_metadata, tracee));
1756+
change_syscall(_metadata, tracee, -1, -ESRCH);
1757+
break;
1758+
case 0x1005:
17451759
/* do nothing (allow getppid) */
17461760
EXPECT_EQ(__NR_getppid, get_syscall(_metadata, tracee));
17471761
break;
@@ -1774,9 +1788,11 @@ void tracer_ptrace(struct __test_metadata *_metadata, pid_t tracee,
17741788
nr = get_syscall(_metadata, tracee);
17751789

17761790
if (nr == __NR_getpid)
1777-
change_syscall(_metadata, tracee, __NR_getppid);
1791+
change_syscall(_metadata, tracee, __NR_getppid, 0);
1792+
if (nr == __NR_gettid)
1793+
change_syscall(_metadata, tracee, -1, 45000);
17781794
if (nr == __NR_openat)
1779-
change_syscall(_metadata, tracee, -1);
1795+
change_syscall(_metadata, tracee, -1, -ESRCH);
17801796
}
17811797

17821798
FIXTURE_DATA(TRACE_syscall) {
@@ -1793,8 +1809,10 @@ FIXTURE_SETUP(TRACE_syscall)
17931809
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1002),
17941810
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_gettid, 0, 1),
17951811
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1003),
1796-
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_getppid, 0, 1),
1812+
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_openat, 0, 1),
17971813
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1004),
1814+
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_getppid, 0, 1),
1815+
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_TRACE | 0x1005),
17981816
BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
17991817
};
18001818

@@ -1842,15 +1860,26 @@ TEST_F(TRACE_syscall, ptrace_syscall_redirected)
18421860
EXPECT_NE(self->mypid, syscall(__NR_getpid));
18431861
}
18441862

1845-
TEST_F(TRACE_syscall, ptrace_syscall_dropped)
1863+
TEST_F(TRACE_syscall, ptrace_syscall_errno)
1864+
{
1865+
/* Swap SECCOMP_RET_TRACE tracer for PTRACE_SYSCALL tracer. */
1866+
teardown_trace_fixture(_metadata, self->tracer);
1867+
self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, NULL,
1868+
true);
1869+
1870+
/* Tracer should skip the open syscall, resulting in ESRCH. */
1871+
EXPECT_SYSCALL_RETURN(-ESRCH, syscall(__NR_openat));
1872+
}
1873+
1874+
TEST_F(TRACE_syscall, ptrace_syscall_faked)
18461875
{
18471876
/* Swap SECCOMP_RET_TRACE tracer for PTRACE_SYSCALL tracer. */
18481877
teardown_trace_fixture(_metadata, self->tracer);
18491878
self->tracer = setup_trace_fixture(_metadata, tracer_ptrace, NULL,
18501879
true);
18511880

1852-
/* Tracer should skip the open syscall, resulting in EPERM. */
1853-
EXPECT_SYSCALL_RETURN(EPERM, syscall(__NR_openat));
1881+
/* Tracer should skip the gettid syscall, resulting fake pid. */
1882+
EXPECT_SYSCALL_RETURN(45000, syscall(__NR_gettid));
18541883
}
18551884

18561885
TEST_F(TRACE_syscall, syscall_allowed)
@@ -1883,7 +1912,21 @@ TEST_F(TRACE_syscall, syscall_redirected)
18831912
EXPECT_NE(self->mypid, syscall(__NR_getpid));
18841913
}
18851914

1886-
TEST_F(TRACE_syscall, syscall_dropped)
1915+
TEST_F(TRACE_syscall, syscall_errno)
1916+
{
1917+
long ret;
1918+
1919+
ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
1920+
ASSERT_EQ(0, ret);
1921+
1922+
ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &self->prog, 0, 0);
1923+
ASSERT_EQ(0, ret);
1924+
1925+
/* openat has been skipped and an errno return. */
1926+
EXPECT_SYSCALL_RETURN(-ESRCH, syscall(__NR_openat));
1927+
}
1928+
1929+
TEST_F(TRACE_syscall, syscall_faked)
18871930
{
18881931
long ret;
18891932

@@ -1894,8 +1937,7 @@ TEST_F(TRACE_syscall, syscall_dropped)
18941937
ASSERT_EQ(0, ret);
18951938

18961939
/* gettid has been skipped and an altered return value stored. */
1897-
EXPECT_SYSCALL_RETURN(EPERM, syscall(__NR_gettid));
1898-
EXPECT_NE(self->mytid, syscall(__NR_gettid));
1940+
EXPECT_SYSCALL_RETURN(45000, syscall(__NR_gettid));
18991941
}
19001942

19011943
TEST_F(TRACE_syscall, skip_after_RET_TRACE)

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