linux-kernel - Re: [PATCH v1 1/4] [RFC] fs/trampfd: Implement the trampoline file descriptor API

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Message-ID: <dc41589a-647a-ba59-5376-abbf5d07c6e7@linux.microsoft.com>
Date:   Tue, 28 Jul 2020 09:58:52 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v1 1/4] [RFC] fs/trampfd: Implement the trampoline file
 descriptor API

Thanks. See inline..

On 7/28/20 9:50 AM, Oleg Nesterov wrote:
> On 07/28, madvenka@...ux.microsoft.com wrote:
>> +bool is_trampfd_vma(struct vm_area_struct *vma)
>> +{
>> +	struct file	*file = vma->vm_file;
>> +
>> +	if (!file)
>> +		return false;
>> +	return !strcmp(file->f_path.dentry->d_name.name, trampfd_name);
> Hmm, this looks obviously wrong or I am totally confused. A user can
> create a file named "[trampfd]", mmap it, and fool trampfd_fault() ?
>
> Why not
>
> 	return file->f_op == trampfd_fops;

This is definitely the correct check. I will fix it.
>
> ?
>
>> +EXPORT_SYMBOL_GPL(is_trampfd_vma);
> why is it exported?

This is in common code and is called by arch code. Should I not export it?
I guess since the symbol is not used by any modules, I don't need to
export it. Please confirm and I will fix this.

Madhavan