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authorOleg Nesterov <oleg@redhat.com>2011-07-21 17:06:53 +0200
committerOleg Nesterov <oleg@redhat.com>2011-07-21 17:06:53 +0200
commit8a35241803eeb0e9fd3fe27835d6b2775c73b641 (patch)
tree09f15db936084e239279844bcb6db6608e2bb06f /kernel
parentf701e5b73a1a79ea62ffd45d9e2bed4c7d5c1fd2 (diff)
ptrace: fix ptrace_signal() && STOP_DEQUEUED interaction
Simple test-case, int main(void) { int pid, status; pid = fork(); if (!pid) { pause(); assert(0); return 0x23; } assert(ptrace(PTRACE_ATTACH, pid, 0,0) == 0); assert(wait(&status) == pid); assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP); kill(pid, SIGCONT); // <--- also clears STOP_DEQUEUD assert(ptrace(PTRACE_CONT, pid, 0,0) == 0); assert(wait(&status) == pid); assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGCONT); assert(ptrace(PTRACE_CONT, pid, 0, SIGSTOP) == 0); assert(wait(&status) == pid); assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP); kill(pid, SIGKILL); return 0; } Without the patch it hangs. After the patch SIGSTOP "injected" by the tracer is not ignored and stops the tracee. Note also that if this test-case uses, say, SIGWINCH instead of SIGCONT, everything works without the patch. This can't be right, and this is confusing. The problem is that SIGSTOP (or any other sig_kernel_stop() signal) has no effect without JOBCTL_STOP_DEQUEUED. This means it is simply ignored after PTRACE_CONT unless JOBCTL_STOP_DEQUEUED was set "by accident", say it wasn't cleared after initial SIGSTOP sent by PTRACE_ATTACH. At first glance we could change ptrace_signal() to add STOP_DEQUEUED after return from ptrace_stop(), but this is not right in case when the tracer does not change the reported SIGSTOP and SIGCONT comes in between. This is even more wrong with PT_SEIZED, SIGCONT adds JOBCTL_TRAP_NOTIFY which will be "lost" during the TRAP_STOP | TRAP_NOTIFY report. So lets add STOP_DEQUEUED _before_ we report the signal. It has no effect unless sig_kernel_stop() == T after the tracer resumes us, and in the latter case the pending STOP_DEQUEUED means no SIGCONT in between, we should stop. Note also that if SIGCONT was sent, PT_SEIZED tracee will correctly report PTRACE_EVENT_STOP/SIGTRAP and thus the tracer can notice the fact SIGSTOP was cancelled. Also, move the current->ptrace check from ptrace_signal() to its caller, get_signal_to_deliver(), this looks more natural. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/signal.c17
1 files changed, 11 insertions, 6 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index 0a1bf2c8bdc..c34f8f899b7 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2084,12 +2084,17 @@ static void do_jobctl_trap(void)
static int ptrace_signal(int signr, siginfo_t *info,
struct pt_regs *regs, void *cookie)
{
- if (!current->ptrace)
- return signr;
-
ptrace_signal_deliver(regs, cookie);
-
- /* Let the debugger run. */
+ /*
+ * We do not check sig_kernel_stop(signr) but set this marker
+ * unconditionally because we do not know whether debugger will
+ * change signr. This flag has no meaning unless we are going
+ * to stop after return from ptrace_stop(). In this case it will
+ * be checked in do_signal_stop(), we should only stop if it was
+ * not cleared by SIGCONT while we were sleeping. See also the
+ * comment in dequeue_signal().
+ */
+ current->jobctl |= JOBCTL_STOP_DEQUEUED;
ptrace_stop(signr, CLD_TRAPPED, 0, info);
/* We're back. Did the debugger cancel the sig? */
@@ -2193,7 +2198,7 @@ relock:
if (!signr)
break; /* will return 0 */
- if (signr != SIGKILL) {
+ if (unlikely(current->ptrace) && signr != SIGKILL) {
signr = ptrace_signal(signr, info,
regs, cookie);
if (!signr)