linux-kernel - Re: [PATCH, for 2.6.29] ptrace: fix the usage of ptrace

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:	Mon, 9 Feb 2009 02:28:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Markus Metzger <markus.t.metzger@...el.com>,
	Roland McGrath <roland@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH, for 2.6.29] ptrace: fix the usage of ptrace_fork()

On 02/09, Oleg Nesterov wrote:
>
> I noticed by pure accident we have ptrace_fork() and friends. This was
> added by "x86, bts: add fork and exit handling", commit
> bf53de907dfdaac178c92d774aae7370d7b97d20

Hmm. Looks like we have more problems here...

"x86, bts: memory accounting", commit c5dee6177f4bd2095aab7d9be9f6ebdddd6deee9.

PTRACE_BTS_CONFIG allocates ->bts_buffer via alloc_locked_buffer()
which updates mm->total_vm/locked_vm.

ptrace_detach() does free_locked_buffer() which "restores" mm->xxx_vm.

But if the tracer exits we are doing __ptrace_unlink()->ptrace_bts_untrace()
which uses a plain kfree(), in that case we don't update mm->xxx_vm ?

Note that the exiting tracer can have sub-threads, so the whole process
does not necessary dies.

Or, the tracer can reap a zombie tracee without PTRACE_DETACH, in that
case we don't update ->mm too.

Oh, and afaics ptrace_detach()->ptrace_bts_detach() can race with the
tracer's sub-thread which does do_wait()->release_task() (if the tracee
was killed before detach takes tasklist), the kernel can crash in this
case.

Unless I missed something, This all looks rather wrong, and I wasn't
aware about these changes :(

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/