On Tue, Sep 29, 2020 at 10:23:50AM -0700, Linus Torvalds wrote:

On Tue, Sep 29, 2020 at 5:16 AM Ondrej Mosnacek [off-list ref] wrote:

quoted

OK, so it seems that reverting comes out as the best choice here.

Yeah.

quoted

BTW, I'm looking at rw_verify_area() and I see this "If (ppos)" check
and the comment above it... And then I look at autofs_write(), which
passes &file->f_pos, while ksys_write() passes file_ppos(file)

Ok, that doesn't matter for the security_file_permission() issue, but
yes, autofs is doing the traditional thing, and it's pointless. Using
file_ppos(file) isn't an option since it's an inline to read_write.c,
but it could just pass in NULL these days and avoid that too.

So how about we just do the appended patch? Can whoever sees this
problem just verify, even though it looks trivially correct...

This looks sensible to me.  I'd throw in a

/* only for autofs, don't use in new code */

near the export, but users of these kind of functions tend to be
blind copy and paste code anyway, so the comment probably isn't
even read by the relevant parties..