linux-kernel - Re: [RFC] Proposal for ptrace improvements

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]

Message-Id: <201103011757.48593.vda.linux@googlemail.com>
Date:	Tue, 1 Mar 2011 17:57:48 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [RFC] Proposal for ptrace improvements

On Tuesday 01 March 2011 16:24, Tejun Heo wrote:
> PROPOSAL
> --------
> ...
> P3. Keep ptrace resume separate from and beneath jctl stop
> 
> As written above, I think the current ptrace behavior, despite a lot
> of rough edges, is in the right direction in that ptrace operates
> beneath jctl.  Therefore, keep the basic operation principles but
> clearly define how jctl and ptrace interacts, or rather, how they
> don't.  The following two rules clearly separate jctl and ptrace.
> 
> * jctl stop initiates when one of the stop signals is received and
>   completes when all the member tasks participate in the group stop,
>   where participation preciesly means that a member task stops in
>   do_signal_stop().  Any member task can only participate once in any
>   given group stop.  ptrace does NOT make any difference in this
>   regard.

This proposal adds a new rule for handling of stop notification
by debuggers. Let's spell it out, because currently strace
doesn't act according to this new rule:

"When waitpid indicates stop on a *stop* signal, then it may be either:
* a signal delivery (strace will inject this signal with PTRACE_SYSCALL(sig));
* or it may be a stop notification, in which case strace *must not*
  try to inject this signal (this would be a bug, it'd make task running).
  Instead, strace should just go back to waiting in waitpid().

These two possibilities can be distinquished by querying
PTRACE_GETSIGINFO. On stop notifications, PTRACE_GETSIGINFO
errors out - stop notification is not a signal delivery
and therefore it has no siginfo."

This is easy to implement (in strace at least).

> * However, PTRACE_DETACH should maintain the integrity of group stop.
>   After a tracee is detached, it should be in a state which is
>   conformant to the current jctl state.  If jctl stop is in effect,
>   the task should be put into TASK_STOPPED; otherwise, TASK_RUNNING.

This means that without changes to gdb, this:

# gdb -p pid_of_application_currently_in_jctl_stop
(gdb) print getpid()
(gdb) print show_me_your_internal_debug_dump()
(gdb) continue

will make application run, whereas this:

# gdb -p pid_of_application_currently_in_jctl_stop
(gdb) print getpid()
(gdb) print show_me_your_internal_debug_dump()
(gdb) quit

will leave application stopped. This looks a bit inconsistent to me.

Do you propose gdb to be chaged so that "continue" command
issues PTRACE_CONT only if gdb knows that application is not
in jctl stop?

-- 
vda
--
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/