linux-kernel - Re: [PATCH] vfs: vfs_tmpfile: ensure O

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Date:   Thu, 3 Nov 2022 20:11:57 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Peter Griffin <peter.griffin@...aro.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <mszeredi@...hat.com>, stable@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Will McVicker <willmcvicker@...gle.com>,
        Peter Griffin <gpeter@...gle.com>
Subject: Re: [PATCH] vfs: vfs_tmpfile: ensure O_EXCL flag is enforced

On Thu, 3 Nov 2022 at 18:04, Peter Griffin <peter.griffin@...aro.org> wrote:
>
> If O_EXCL is *not* specified, then linkat() can be
> used to link the temporary file into the filesystem.
> If O_EXCL is specified then linkat() should fail (-1).
>
> After commit 863f144f12ad ("vfs: open inside ->tmpfile()")
> the O_EXCL flag is no longer honored by the vfs layer for
> tmpfile, which means the file can be linked even if O_EXCL
> flag is specified, which is a change in behaviour for
> userspace!
>
> The open flags was previously passed as a parameter, so it
> was uneffected by the changes to file->f_flags caused by
> finish_open(). This patch fixes the issue by storing
> file->f_flags in a local variable so the O_EXCL test
> logic is restored.
>
> This regression was detected by Android CTS Bionic fcntl()
> tests running on android-mainline [1].
>
> [1] https://android.googlesource.com/platform/bionic/+/
>     refs/heads/master/tests/fcntl_test.cpp#352

Looks good.

Acked-by: Miklos Szeredi <mszeredi@...hat.com>

Thanks,
Miklos
>