From f3eb9f3541b27da3d34167074ecc689798af5d9a Mon Sep 17 00:00:00 2001
From: jhb <jhb@ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f>
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.


git-svn-id: svn://svn.freebsd.org/base/stable/10@342704 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
---
 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 16cea06b8..daf91d385 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2803,6 +2803,8 @@ issignal(struct thread *td)
 			sig = ptracestop(td, sig, &td->td_dbgksi);
 			mtx_lock(&ps->ps_mtx);
 
+			td->td_dbgksi.ksi_signo = 0;
+
 			/* 
 			 * Keep looking if the debugger discarded the signal
 			 * or replaced it with a masked signal.
diff --git a/tests/sys/kern/ptrace_test.c b/tests/sys/kern/ptrace_test.c
index 407c62a8c..850c84c88 100644
--- a/tests/sys/kern/ptrace_test.c
+++ b/tests/sys/kern/ptrace_test.c
@@ -3112,6 +3112,78 @@ 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)
 {
 
@@ -3161,6 +3233,7 @@ ATF_TP_ADD_TCS(tp)
 #if defined(__amd64__) || defined(__i386__)
 	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