Messages in this thread Patch in this message |  | | | From | Tejun Heo <> | | Subject | [PATCH 12/17] ptrace: implement PTRACE_INTERRUPT | | Date | Mon, 30 May 2011 01:12:35 +0200 |
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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> --- include/linux/ptrace.h | 1 + kernel/ptrace.c | 29 +++++++++++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-) diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index 67ad3f1..ad754d1 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 07505aa..d5e38ac 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -657,10 +657,12 @@ 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: @@ -693,6 +695,27 @@ 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; @@ -818,7 +841,8 @@ 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; @@ -960,7 +984,8 @@ 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); -- 1.7.5.2
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