From 261ef81beafdd345090d5fd259ab07f4ab26ff2a Mon Sep 17 00:00:00 2001
From: jhb <jhb@FreeBSD.org>
Date: Wed, 2 Jan 2019 19:11:49 +0000
Subject: [PATCH] MFC 341800: Don't report stale signal information in
 ptrace_lwpinfo.

Once a signal's siginfo was copied to 'td_si' as part of the signal
exchange in issignal(), it was never cleared.  This caused future
thread events that are reported as SIGTRAP events without signal
information to report the stale siginfo in 'td_si'.  For example, if a
debugger created a new process and used SIGSTOP to stop it after
PT_ATTACH, future system call entry / exit events would set PL_FLAG_SI
with the SIGSTOP siginfo in pl_siginfo.  This broke 'catch syscall' in
current versions of gdb as it assumed PL_FLAG_SI with SIGTRAP
indicates a breakpoint or single step trap.
---
 sys/kern/kern_sig.c          |  2 +
 tests/sys/kern/ptrace_test.c | 73 ++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 3296a7e9e66..3854b201a4b 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2858,6 +2858,8 @@ issignal(struct thread *td)
 			sig = ptracestop(td, sig, &ksi);
 			mtx_lock(&ps->ps_mtx);
 
+			td->td_si.si_signo = 0;
+
 			/* 
 			 * Keep looking if the debugger discarded or
 			 * replaced the signal.
diff --git a/tests/sys/kern/ptrace_test.c b/tests/sys/kern/ptrace_test.c
index ef098e71ffd..c5fd443b85c 100644
--- a/tests/sys/kern/ptrace_test.c
+++ b/tests/sys/kern/ptrace_test.c
@@ -3772,6 +3772,78 @@ ATF_TC_BODY(ptrace__PT_CONTINUE_different_thread, tc)
 }
 #endif
 
+/*
+ * Verify that PT_LWPINFO doesn't return stale siginfo.
+ */
+ATF_TC_WITHOUT_HEAD(ptrace__PT_LWPINFO_stale_siginfo);
+ATF_TC_BODY(ptrace__PT_LWPINFO_stale_siginfo, tc)
+{
+	struct ptrace_lwpinfo pl;
+	pid_t fpid, wpid;
+	int events, status;
+
+	ATF_REQUIRE((fpid = fork()) != -1);
+	if (fpid == 0) {
+		trace_me();
+		raise(SIGABRT);
+		exit(1);
+	}
+
+	/* The first wait() should report the stop from SIGSTOP. */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(wpid == fpid);
+	ATF_REQUIRE(WIFSTOPPED(status));
+	ATF_REQUIRE(WSTOPSIG(status) == SIGSTOP);
+
+	ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+	/* The next stop should report the SIGABRT in the child body. */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(wpid == fpid);
+	ATF_REQUIRE(WIFSTOPPED(status));
+	ATF_REQUIRE(WSTOPSIG(status) == SIGABRT);
+
+	ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+	ATF_REQUIRE(pl.pl_flags & PL_FLAG_SI);
+	ATF_REQUIRE(pl.pl_siginfo.si_signo == SIGABRT);
+
+	/*
+	 * Continue the process ignoring the signal, but enabling
+	 * syscall traps.
+	 */
+	ATF_REQUIRE(ptrace(PT_SYSCALL, fpid, (caddr_t)1, 0) == 0);
+
+	/*
+	 * The next stop should report a system call entry from
+	 * exit().  PL_FLAGS_SI should not be set.
+	 */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(wpid == fpid);
+	ATF_REQUIRE(WIFSTOPPED(status));
+	ATF_REQUIRE(WSTOPSIG(status) == SIGTRAP);
+
+	ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+	ATF_REQUIRE(pl.pl_flags & PL_FLAG_SCE);
+	ATF_REQUIRE((pl.pl_flags & PL_FLAG_SI) == 0);
+
+	/* Disable syscall tracing and continue the child to let it exit. */
+	ATF_REQUIRE(ptrace(PT_GET_EVENT_MASK, fpid, (caddr_t)&events,
+	    sizeof(events)) == 0);
+	events &= ~PTRACE_SYSCALL;
+	ATF_REQUIRE(ptrace(PT_SET_EVENT_MASK, fpid, (caddr_t)&events,
+	    sizeof(events)) == 0);
+	ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+	/* The last event should be for the child process's exit. */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(WIFEXITED(status));
+	ATF_REQUIRE(WEXITSTATUS(status) == 1);
+
+	wpid = wait(&status);
+	ATF_REQUIRE(wpid == -1);
+	ATF_REQUIRE(errno == ECHILD);
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
@@ -3831,6 +3903,7 @@ ATF_TP_ADD_TCS(tp)
 #if defined(HAVE_BREAKPOINT) && defined(SKIP_BREAK)
 	ATF_TP_ADD_TC(tp, ptrace__PT_CONTINUE_different_thread);
 #endif
+	ATF_TP_ADD_TC(tp, ptrace__PT_LWPINFO_stale_siginfo);
 
 	return (atf_no_error());
 }
-- 
2.45.0