On Thu, May 02, 2024 at 05:41:23PM -0700, Kees Cook wrote: > On Fri, May 03, 2024 at 01:14:45AM +0100, Al Viro wrote: > > On Thu, May 02, 2024 at 05:10:18PM -0700, Kees Cook wrote: > > > > > But anyway, there needs to be a general "oops I hit 0"-aware form of > > > get_file(), and it seems like it should just be get_file() itself... > > > > ... which brings back the question of what's the sane damage mitigation > > for that. Adding arseloads of never-exercised failure exits is generally > > a bad idea - it's asking for bitrot and making the thing harder to review > > in future. > > Linus seems to prefer best-effort error recovery to sprinkling BUG()s > around. But if that's really the solution, then how about get_file() > switching to to use inc_not_zero and BUG on 0?
Making get_file() return an error is not an option. For all current callers that's pointless churn for a condition that's not supposed to happen at all. Additionally, iirc *_inc_not_zero() variants are implemented with try_cmpxchg() which scales poorly under contention for a condition that's not supposed to happen.
