On Fri, Sep 22, 2023 at 11:25:56AM -0700, Shakeel Butt wrote: > On Fri, Sep 22, 2023 at 10:53 AM Kees Cook <keesc...@chromium.org> wrote: > > > > Prepare for the coming implementation by GCC and Clang of the __counted_by > > attribute. Flexible array members annotated with __counted_by can have > > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS > > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family > > functions). > > > > As found with Coccinelle[1], add __counted_by for struct > > mem_cgroup_threshold_ary. > > > > [1] > > https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci > > > > Cc: Andrew Morton <a...@linux-foundation.org> > > Cc: Shakeel Butt <shake...@google.com> > > Cc: Roman Gushchin <roman.gushc...@linux.dev> > > Cc: Johannes Weiner <han...@cmpxchg.org> > > Cc: Michal Hocko <mho...@suse.com> > > Cc: "Matthew Wilcox (Oracle)" <wi...@infradead.org> > > Signed-off-by: Kees Cook <keesc...@chromium.org> > > --- > > include/linux/memcontrol.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > index 45d0c10e86cc..e0cfab58ab71 100644 > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -143,7 +143,7 @@ struct mem_cgroup_threshold_ary { > > /* Size of entries[] */ > > unsigned int size; > > /* Array of thresholds */ > > - struct mem_cgroup_threshold entries[]; > > + struct mem_cgroup_threshold entries[] __counted_by(size); > > Does 'size' here have to be a member of the same struct as entries? We > have nodeinfo[] in struct mem_cgroup whose size is nr_node_ids which > is global. Will __counted_by() work for that?
Not presently, no. This may come in future expansions of the feature. We're also hoping to gain expressions for places where a size isn't a native count, like for big endian, or a byte count that includes the entire struct, etc. For now, though, the feature is narrowly scoped just to get the common case landed. -Kees -- Kees Cook
