[PATCH 05/13] fs: check FMODE_WRITE in __kernel_write

[Christoph Hellwig]

On Mon, Jun 15, 2020 at 09:39:31AM -0700, Linus Torvalds wrote:
> On Mon, Jun 15, 2020 at 5:13 AM Christoph Hellwig <hch at lst.de> wrote:
> >
> > We still need to check if the fѕ is open write, even for the low-level
> > helper.
> 
> Is there actually a way to trigger something like this? I'm wondering
> if it's worth a WARN_ON_ONCE()?
> 
> It doesn't sound sensible to have some kernel functionality try to
> write to a file it didn't open for write, and sounds like a kernel bug
> if this case were to ever trigger..

Yes, this would be bug in the calling code.