linux-kernel - Re: [PATCHSET RFC] ptrace,signal: clean transition between STOPPED and TRACED

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 13 Jan 2011 16:51:20 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, roland@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCHSET RFC] ptrace,signal: clean transition between STOPPED
	and TRACED

On 01/12, Jan Kratochvil wrote:
>
> FSF GDB for `T (stopped)' processes currently does:
>   PTRACE_ATTACH
>   check /proc/%d/status for `T (stopped)' (by GDB's pid_is_stopped)
>     if found then kill (PID, SIGSTOP) && ptrace (PTRACE_CONT, PID, 0, 0).
>   waitpid (pid, &status, 0) - so that this one does not get stuck if the stop
>                               event was already eaten out before.
>
> If the `T (stopped)' will now always FAIL then at leat the waitpid then should
> never get stuck.

I think it won't stuck. With this change the tracee always goes from
TASK_STOPPED to TASK_TRACED with the correct (and nonzero) stop code.

Btw, this should fix the case when ->exit_code was already consumed
by the previous debugger.

> FSF gdbserver --multi does PTRACE_ATTACH followed by waitpid (WNOHANG) and it
> fails if it returns ECHILD on the first try.

Not sure I understand... With or without this change waitpid()
shouldn't return ECHILD. But (again, with or without this change)
it can return 0 due to WNOHANG.

> 	ptrace(PTRACE_ATTACH, 22049, 0, 0)      = 0
> 	wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSTOP}], WNOHANG, NULL) = 22049
>
> It may be also a gdbserver bug, though.

I do not know if this matters or not, but just in case...

gdb shouldn't assume the tracee will report SIGSTOP after attach.
Yes, PTRACE_ATTACH sends this signal implicitly, but the tracee can
dequeue and report another pending signal before SIGSTOP.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/