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authorTejun Heo <tj@kernel.org>2011-06-14 11:20:16 +0200
committerOleg Nesterov <oleg@redhat.com>2011-06-16 21:41:53 +0200
commitfca26f260c528ee51a2e451b5b200aeb528f3e09 (patch)
tree8c64ecdcece48b55e79bbb7f376a834fc99804a3
parent3544d72a0e10d0aa1c1bd59ed77a53a59cdc12f7 (diff)
ptrace: implement PTRACE_INTERRUPT
Currently, there's no way to trap a running ptracee short of sending a signal which has various side effects. This patch implements PTRACE_INTERRUPT which traps ptracee without any signal or job control related side effect. The implementation is almost trivial. It uses the group stop trap - SIGTRAP | PTRACE_EVENT_STOP << 8. A new trap flag JOBCTL_TRAP_INTERRUPT is added, which is set on PTRACE_INTERRUPT and cleared when any trap happens. As INTERRUPT should be useable regardless of the current state of tracee, task_is_traced() test in ptrace_check_attach() is skipped for INTERRUPT. PTRACE_INTERRUPT is available iff tracee is attached with PTRACE_SEIZE. Test program follows. #define PTRACE_SEIZE 0x4206 #define PTRACE_INTERRUPT 0x4207 #define PTRACE_SEIZE_DEVEL 0x80000000 static const struct timespec ts100ms = { .tv_nsec = 100000000 }; static const struct timespec ts1s = { .tv_sec = 1 }; static const struct timespec ts3s = { .tv_sec = 3 }; int main(int argc, char **argv) { pid_t tracee; tracee = fork(); if (tracee == 0) { nanosleep(&ts100ms, NULL); while (1) { printf("tracee: alive pid=%d\n", getpid()); nanosleep(&ts1s, NULL); } } if (argc > 1) kill(tracee, SIGSTOP); nanosleep(&ts100ms, NULL); ptrace(PTRACE_SEIZE, tracee, NULL, (void *)(unsigned long)PTRACE_SEIZE_DEVEL); if (argc > 1) { waitid(P_PID, tracee, NULL, WSTOPPED); ptrace(PTRACE_CONT, tracee, NULL, NULL); } nanosleep(&ts3s, NULL); printf("tracer: INTERRUPT and DETACH\n"); ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL); waitid(P_PID, tracee, NULL, WSTOPPED); ptrace(PTRACE_DETACH, tracee, NULL, NULL); nanosleep(&ts3s, NULL); printf("tracer: exiting\n"); kill(tracee, SIGKILL); return 0; } When called without argument, tracee is seized from running state, interrupted and then detached back to running state. # ./test-interrupt tracee: alive pid=4546 tracee: alive pid=4546 tracee: alive pid=4546 tracer: INTERRUPT and DETACH tracee: alive pid=4546 tracee: alive pid=4546 tracee: alive pid=4546 tracer: exiting When called with argument, tracee is seized from stopped state, continued, interrupted and then detached back to stopped state. # ./test-interrupt 1 tracee: alive pid=4548 tracee: alive pid=4548 tracee: alive pid=4548 tracer: INTERRUPT and DETACH tracer: exiting Before PTRACE_INTERRUPT, once the tracee was running, there was no way to trap tracee and do PTRACE_DETACH without causing side effect. -v2: Updated to use task_set_jobctl_pending() so that it doesn't end up scheduling TRAP_STOP if child is dying which may make the child unkillable. Spotted by Oleg. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com>
-rw-r--r--include/linux/ptrace.h1
-rw-r--r--kernel/ptrace.c29
2 files changed, 28 insertions, 2 deletions
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 67ad3f152329..ad754d1e0b13 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -48,6 +48,7 @@
#define PTRACE_SETREGSET 0x4205
#define PTRACE_SEIZE 0x4206
+#define PTRACE_INTERRUPT 0x4207
/* flags in @data for PTRACE_SEIZE */
#define PTRACE_SEIZE_DEVEL 0x80000000 /* temp flag for development */
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index dcf9f974198c..6852c0f4a916 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -658,10 +658,12 @@ static int ptrace_regset(struct task_struct *task, int req, unsigned int type,
int ptrace_request(struct task_struct *child, long request,
unsigned long addr, unsigned long data)
{
+ bool seized = child->ptrace & PT_SEIZED;
int ret = -EIO;
siginfo_t siginfo;
void __user *datavp = (void __user *) data;
unsigned long __user *datalp = datavp;
+ unsigned long flags;
switch (request) {
case PTRACE_PEEKTEXT:
@@ -694,6 +696,27 @@ int ptrace_request(struct task_struct *child, long request,
ret = ptrace_setsiginfo(child, &siginfo);
break;
+ case PTRACE_INTERRUPT:
+ /*
+ * Stop tracee without any side-effect on signal or job
+ * control. At least one trap is guaranteed to happen
+ * after this request. If @child is already trapped, the
+ * current trap is not disturbed and another trap will
+ * happen after the current trap is ended with PTRACE_CONT.
+ *
+ * The actual trap might not be PTRACE_EVENT_STOP trap but
+ * the pending condition is cleared regardless.
+ */
+ if (unlikely(!seized || !lock_task_sighand(child, &flags)))
+ break;
+
+ if (likely(task_set_jobctl_pending(child, JOBCTL_TRAP_STOP)))
+ signal_wake_up(child, 0);
+
+ unlock_task_sighand(child, &flags);
+ ret = 0;
+ break;
+
case PTRACE_DETACH: /* detach a process that was attached. */
ret = ptrace_detach(child, data);
break;
@@ -819,7 +842,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
goto out_put_task_struct;
}
- ret = ptrace_check_attach(child, request == PTRACE_KILL);
+ ret = ptrace_check_attach(child, request == PTRACE_KILL ||
+ request == PTRACE_INTERRUPT);
if (ret < 0)
goto out_put_task_struct;
@@ -961,7 +985,8 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
goto out_put_task_struct;
}
- ret = ptrace_check_attach(child, request == PTRACE_KILL);
+ ret = ptrace_check_attach(child, request == PTRACE_KILL ||
+ request == PTRACE_INTERRUPT);
if (!ret)
ret = compat_arch_ptrace(child, request, addr, data);