On Wed, Nov 28, 2018 at 01:35:46PM +0100, Oleg Nesterov wrote: > On 11/28, Dmitry V. Levin wrote: > > > > > Just like ptrace_request(PTRACE_LISTEN) > > > does but you can do this lockless (no need to lock_task_sighand()). > > > > Why this can be done lockless? All other places in that file do > > the locking, > > PTRACE_LISTEN too doesn't need lock_task_sighand() to access ->last_siginfo, > this code predates ptrace_freeze_traced() which ensures that the tracee can't > go away and clear ->last_siginfo. > > However, unlike ptrace_get_syscall(), PTRACE_LISTEN needs spin_lock_irq(siglock), > it modifies ->jobctl and calls signal_wake_up(). What about PTRACE_GETSIGINFO? Can it also be done lockless because ptrace_check_attach() has already called ptrace_freeze_traced()? > > > Of course, debugger can do PTRACE_SETSIGINFO and confuse itself but probably we > > > do not care? > > > > The only potential issue I could think of is whether PTRACE_SETSIGINFO > > could be used this way to cause an information leak by making > > PTRACE_GET_SYSCALL_INFO access some unrelated data. > > Well, afaics ptrace_get_syscall() does nothing "special", debugger can use other > PTRACE_ requests to get the same info? I agree. -- ldv
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