linux-kernel - Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old

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Message-ID: <AM6PR03MB5170C3A4319BA6A057C3CCACE4FE0@AM6PR03MB5170.eurprd03.prod.outlook.com>
Date:   Mon, 9 Mar 2020 19:34:59 +0000
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
CC:     Christian Brauner <christian.brauner@...ntu.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Yuyang Du <duyuyang@...il.com>,
        David Hildenbrand <david@...hat.com>,
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        Aleksa Sarai <cyphar@...har.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
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Subject: Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in
 flush_old_exec

On 3/8/20 10:38 PM, Eric W. Biederman wrote:
> 
> I have read through the code in exec_mmap and I do not see anything
> that depends on sighand or the sighand lock, or on signals in anyway
> so this should be safe.
> 
> This rearrangement of code has two siginficant benefits.  It makes
                                        ^ typo: significant

> the determination of passing the point of no return by testing bprm->mm
> accurate.  All failures prior to that point in flush_old_exec are
> either truly recoverable or they are fatal.
> 
> Futher this consolidates all of the possible indefinite waits for   ^ typo: Further

> userspace together at the top of flush_old_exec.  The possible wait
> for a ptracer on PTRACE_EVENT_EXIT, the possible wait for a page fault
> to be resolved in clear_child_tid, and the possible wait for a page
> fault in exit_robust_list.
> 
> This consolidation allows the creation of a mutex to replace
> cred_guard_mutex that is not held of possible indefinite userspace

can you also reword this "held of" thing here as well?


Thanks
Bernd.