On Fri, Oct 09, 2020 at 09:55:56AM -0600, Shuah Khan wrote: > Introduce Simple atomic counters. > > There are a number of atomic_t usages in the kernel where atomic_t api > is used strictly for counting and not for managing object lifetime. In > some cases, atomic_t might not even be needed. > > The purpose of these counters is to clearly differentiate atomic_t > counters from atomic_t usages that guard object lifetimes, hence prone > to overflow and underflow errors. It allows tools that scan for underflow > and overflow on atomic_t usages to detect overflow and underflows to scan > just the cases that are prone to errors. > > Simple atomic counters api provides interfaces for simple atomic counters > that just count, and don't guard resource lifetimes. The interfaces are > built on top of atomic_t api, providing a smaller subset of atomic_t > interfaces necessary to support simple counters. > > Counter wraps around to INT_MIN when it overflows and should not be used > to guard resource lifetimes, device usage and open counts that control > state changes, and pm states. Overflowing to INT_MIN is consistent with > the atomic_t api, which it is built on top of. > > Using counter_atomic* to guard lifetimes could lead to use-after free > when it overflows and undefined behavior when used to manage state > changes and device usage/open states. > > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
