linux-kernel - Re: [PATCH v6 14/16] pidfd: Use new infrastructure to fix deadlocks in execve

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Message-ID: <20200325154013.jkpkwer3y7c6kr64@wittgenstein>
Date:   Wed, 25 Mar 2020 16:40:13 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Bernd Edlinger <bernd.edlinger@...mail.de>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        "jannh@...gle.com" <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "adobriyan@...il.com" <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        "avagin@...il.com" <avagin@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
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        David Hildenbrand <david@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
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        Jason Gunthorpe <jgg@...pe.ca>,
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        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v6 14/16] pidfd: Use new infrastructure to fix deadlocks
 in execve

On Sat, Mar 21, 2020 at 02:46:16AM +0000, Bernd Edlinger wrote:
> This changes __pidfd_fget to use the new exec_update_mutex
> instead of cred_guard_mutex.
> 
> This should be safe, as the credentials do not change
> before exec_update_mutex is locked.  Therefore whatever
> file access is possible with holding the cred_guard_mutex
> here is also possbile with the exec_update_mutex.
> 
> Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>

Reviewed-by: Christian Brauner <christian.brauner@...ntu.com>