Messages in this thread | | | From | "Eric W. Biederman" <> | Date | Tue, 03 May 2022 14:36:55 -0500 | Subject | Re: [PATCH v2 06/12] ptrace: Reimplement PTRACE_KILL by always sending SIGKILL |
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Oleg Nesterov <oleg@redhat.com> writes:
> On 04/29, Eric W. Biederman wrote: >> >> Call send_sig_info in PTRACE_KILL instead of ptrace_resume. Calling >> ptrace_resume is not safe to call if the task has not been stopped >> with ptrace_freeze_traced. > > Oh, I was never, never able to understand why do we have PTRACE_KILL > and what should it actually do. > > I suggested many times to simply remove it but OK, we probably can't > do this.
I thought I remembered you suggesting fixing it in some other way.
I took at quick look in codesearch.debian.net and PTRACE_KILL is definitely in use. I find uses in gcc-10, firefox-esr_91.8, llvm_toolchain, qtwebengine. At which point I stopped looking.
>> --- a/kernel/ptrace.c >> +++ b/kernel/ptrace.c >> @@ -1238,7 +1238,7 @@ int ptrace_request(struct task_struct *child, long request, >> case PTRACE_KILL: >> if (child->exit_state) /* already dead */ >> return 0; >> - return ptrace_resume(child, request, SIGKILL); >> + return send_sig_info(SIGKILL, SEND_SIG_NOINFO, child); > > Note that currently ptrace(PTRACE_KILL) can never fail (yes, yes, it > is unsafe), but send_sig_info() can. If we do not remove PTRACE_KILL, > then I'd suggest > > case PTRACE_KILL: > if (!child->exit_state) > send_sig_info(SIGKILL); > return 0; > > to make this change a bit more compatible.
Quite. The only failure I can find from send_sig_info is if lock_task_sighand fails and PTRACE_KILL is deliberately ignoring errors when the target task has exited.
case PTRACE_KILL: send_sig_info(SIGKILL); return 0;
I think that should suffice.
> Also, please remove the note about PTRACE_KILL in > set_task_blockstep().
Good catch, thank you.
Eric
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