Oleg Nesterov <oleg@xxxxxxxxxx> 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
