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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Kees Cook' <keescook@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Subject: RE: [PATCH v4 03/11] fs: Add fd_install_received() wrapper for
 __fd_install_received()
Thread-Topic: [PATCH v4 03/11] fs: Add fd_install_received() wrapper for
 __fd_install_received()
Thread-Index: AQHWQ44F2CX108LjrkCobo2loVeUYajc8NxQ
Date:   Wed, 17 Jun 2020 15:35:20 +0000
Message-ID: <6de12195ec3244b99e6026b4b46e5be2@AcuMS.aculab.com>
References: <20200616032524.460144-1-keescook@chromium.org>
 <20200616032524.460144-4-keescook@chromium.org>
In-Reply-To: <20200616032524.460144-4-keescook@chromium.org>
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From: Kees Cook
> Sent: 16 June 2020 04:25
> 
> For both pidfd and seccomp, the __user pointer is not used. Update
> __fd_install_received() to make writing to ufd optional. (ufd
> itself cannot checked for NULL because this changes the SCM_RIGHTS
> interface behavior.) In these cases, the new fd needs to be returned
> on success.  Update the existing callers to handle it. Add new wrapper
> fd_install_received() for pidfd and seccomp that does not use the ufd
> argument.
...> 
>  static inline int fd_install_received_user(struct file *file, int __user *ufd,
>  					   unsigned int o_flags)
>  {
> -	return __fd_install_received(file, ufd, o_flags);
> +	return __fd_install_received(file, true, ufd, o_flags);
> +}

Can you get rid of the 'return user' parameter by adding
	if (!ufd) return -EFAULT;
to the above wrapper, then checking for NULL in the function?

Or does that do the wrong horrid things in the fail path?

	David

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