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