linux-kernel - Re: [REPOST PATCH v3 0/2] vfs: fix a mount table handling problem

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Message-ID: <7064c4cc-4098-6744-298d-fddb3621ca41@themaw.net>
Date:   Wed, 21 Sep 2022 12:38:15 +0800
From:   Ian Kent <raven@...maw.net>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Siddhesh Poyarekar <siddhesh@...plt.org>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [REPOST PATCH v3 0/2] vfs: fix a mount table handling problem


On 21/9/22 09:20, Theodore Ts'o wrote:
> On Tue, Sep 20, 2022 at 03:26:17PM +0800, Ian Kent wrote:
>> Whenever a mount has an empty "source" (aka mnt_fsname), the glibc
>> function getmntent incorrectly parses its input, resulting in reporting
>> incorrect data to the caller.
>>
>> The problem is that the get_mnt_entry() function in glibc's
>> misc/mntent_r.c assumes that leading whitespace on a line can always
>> be discarded because it will always be followed by a # for the case
>> of a comment or a non-whitespace character that's part of the value
>> of the first field. However, this assumption is violated when the
>> value of the first field is an empty string.
>>
>> This is fixed in the mount API code by simply checking for a pointer
>> that contains a NULL and treating it as a NULL pointer.
> Why not simply have the mount API code disallow a zero-length "source"
> / mnt_fsname?

Hi Ted,


I suppose but it seems to me that, for certain file systems, mostly

pseudo file systems, the source isn't needed and is left out ... so

disallowing a zero length source could lead to quite a bit of breakage.


Ian