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To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20190212145450.2200-1-demiobenour@gmail.com>
 <20190212145450.2200-4-demiobenour@gmail.com>
 <20190212203809.GK2217@ZenIV.linux.org.uk>
From:   "Demi M. Obenour" <demiobenour@gmail.com>
Openpgp: preference=signencrypt
Subject: Re: [PATCH 4/4] Return -EINVAL if userspace passes bogus flags to
 open()
Message-ID: <ce981281-bb3a-a539-8d5a-b2d88107d4c0@gmail.com>
Date:   Tue, 12 Feb 2019 18:00:44 -0500
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From: "Demi M. Obenour" <demiobenour@gmail.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: "open list:FILESYSTEMS (VFS and infrastructure)"
 <linux-fsdevel@vger.kernel.org>, open list <linux-kernel@vger.kernel.org>
Message-ID: <ce981281-bb3a-a539-8d5a-b2d88107d4c0@gmail.com>
Subject: Re: [PATCH 4/4] Return -EINVAL if userspace passes bogus flags to
 open()
References: <20190212145450.2200-1-demiobenour@gmail.com>
 <20190212145450.2200-4-demiobenour@gmail.com>
 <20190212203809.GK2217@ZenIV.linux.org.uk>
In-Reply-To: <20190212203809.GK2217@ZenIV.linux.org.uk>

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On 2/12/19 3:38 PM, Al Viro wrote:
> On Tue, Feb 12, 2019 at 09:54:47AM -0500, demiobenour@gmail.com wrote:
>> From: "Demi M. Obenour" <demiobenour@gmail.com>
>>
>> While testing the O_PATHSTATIC patch, I discovered that Linux does not=

>> return any error if an invalid flag is passed to open(2).  This preven=
ts
>> adding new flags without a (minor) risk of breaking userspace.
>> Therefore, add a check for invalid flags, and return -EINVAL if any ar=
e
>> found.
>=20
> ... which would qualtify as userland ABI breakage all by itself.
>=20
I suspect that very few (if any) programs pass invalid flags to open().
Additionally, O_DIRECT was added in Linux 2.4, even though it had
previously been ignored.  If someone knows of a real program that does,
I can instead create an open2() syscall, but I would prefer to avoid that=
=2E


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