selftests/seccomp: Remove SIGSTOP si_pid check

Commit f149b3155744 ("signal: Never allocate siginfo for SIGKILL or SIGSTOP") means that the seccomp selftest cannot check si_pid under SIGSTOP anymore. Since it's believed[1] there are no other userspace things depending on the old behavior, this removes the behavioral check in the selftest, since it's more a "extra" sanity check (which turns out, maybe, not to have been useful to test).

[1] https://lkml.kernel.org/r/CAGXu5jJaZAOzP1qFz66tYrtbuywqb+UN2SOA1VLHpCCOiYvYeg at mail.gmail.com

Reported-by Tycho Andersen <tycho at tycho.ws>

Suggested-by Eric W. Biederman <ebiederm at xmission.com>

Signed-off-by Kees Cook <keescook at chromium.org>

---
Shuah, can you make sure that Linus gets this before v4.20 is released? Thanks!

---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

tools/testing/selftests/seccomp/seccomp_bpf.c +7 -3

index e1473234968d..c9a2abf8be1b 100644
@@ -2731,9 +2731,14 @@ TEST(syscall_restart)
        ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
        ASSERT_EQ(true, WIFSTOPPED(status));
        ASSERT_EQ(SIGSTOP, WSTOPSIG(status));
-       /* Verify signal delivery came from parent now. */
        ASSERT_EQ(0, ptrace(PTRACE_GETSIGINFO, child_pid, NULL, &info));
-       EXPECT_EQ(getpid(), info.si_pid);
+       /*
+        * There is no siginfo on SIGSTOP any more, so we can't verify
+        * signal delivery came from parent now (getpid() == info.si_pid).
+        * https://lkml.kernel.org/r/CAGXu5jJaZAOzP1qFz66tYrtbuywqb+UN2SOA1VLHpCCOiYvYeg at mail.gmail.com
+        * At least verify the SIGSTOP via PTRACE_GETSIGINFO.
+        */
+       EXPECT_EQ(SIGSTOP, info.si_signo);
 
        /* Restart nanosleep with SIGCONT, which triggers restart_syscall. */
        ASSERT_EQ(0, kill(child_pid, SIGCONT));
--

2.17.1

--
Kees Cook

Quoted 10 lines · Kees Cook

Commit f149b3155744 ("signal: Never allocate siginfo for SIGKILL or SIGSTOP") means that the seccomp selftest cannot check si_pid under SIGSTOP anymore. Since it's believed[1] there are no other userspace things depending on the old behavior, this removes the behavioral check in the selftest, since it's more a "extra" sanity check (which turns out, maybe, not to have been useful to test).

[1] https://lkml.kernel.org/r/CAGXu5jJaZAOzP1qFz66tYrtbuywqb+UN2SOA1VLHpCCOiYvYeg at mail.gmail.com

Quoted 5 lines

Reported-by Tycho Andersen <tycho at tycho.ws>

Suggested-by Eric W. Biederman <ebiederm at xmission.com>

Signed-off-by Kees Cook <keescook at chromium.org>

---
Shuah, can you make sure that Linus gets this before v4.20 is released? Thanks!

Ping. Shuah, can you get this to Linus (or should I send it directly?)