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Don't report stale signal information for non-signal events in ptrace_lwpinfo.

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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.

Reviewed by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D18487
This commit is contained in:
John Baldwin 2018-12-10 19:39:24 +00:00
parent a895c1c28a
commit c5786670ac
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=341800
2 changed files with 75 additions and 0 deletions
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2
sys/kern/kern_sig.c
View File

@ -2847,6 +2847,8 @@ 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.

73
tests/sys/kern/ptrace_test.c
View File

@ -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());
}