Re: [PATCH] vfs: vfs_tmpfile: ensure O_EXCL flag is enforced

[Miklos Szeredi]

On Thu, 3 Nov 2022 at 18:04, Peter Griffin <peter.griffin@xxxxxxxxxx> 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@xxxxxxxxxx>

Thanks,
Miklos
>