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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
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        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrei Vagin <avagin@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
        Yuyang Du <duyuyang@gmail.com>,
        David Hildenbrand <david@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
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        James Morris <jamorris@linux.microsoft.com>,
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        Shakeel Butt <shakeelb@google.com>,
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        Christian Kellner <christian@kellner.me>,
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Date:   Mon, 09 Mar 2020 15:35:42 -0500
In-Reply-To: <AM6PR03MB5170E548767878B3E454756AE4FE0@AM6PR03MB5170.eurprd03.prod.outlook.com>
        (Bernd Edlinger's message of "Mon, 9 Mar 2020 20:03:46 +0000")
Message-ID: <87sgihxo4h.fsf@x220.int.ebiederm.org>
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Subject: Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old_exec
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Bernd Edlinger <bernd.edlinger@hotmail.de> writes:

> On 3/9/20 8:58 PM, Eric W. Biederman wrote:
>> 
>> Ok.  I think this has it sorted:
>> 
>>     exec: Move exec_mmap right after de_thread in flush_old_exec
>>     
>>     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 significant benefits.  It makes
>>     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.
>>     
>>     Further this consolidates all of the possible indefinite waits for
>>     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 over possible indefinite userspace
>>     waits.  Which will allow removing deadlock scenarios from the kernel.
>>     
>>     Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
>>     Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>> 
>> 
>> I don't think I usually have this many typos.  Sigh.
>> 
>
> OK.
>
> never mind,

No no.  I really appreciate all of the scrutiny.  Frequently the issues
that will produce typos or poor patch descriptions are also the issues
that will produce sloppy patches as well.  I was just frustrated with
myself.

Eric