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1. With CONFIG_JUMP_LABEL=n static_key_slow_inc() doesn't have any
protection against key->enabled refcounter overflow.
2. With CONFIG_JUMP_LABEL=y static_key_slow_inc_cpuslocked()
still may turn the refcounter negative as (v + 1) may overflow.
key->enabled is indeed a ref-counter as it's documented in multiple
places: top comment in jump_label.h, Documentation/staging/static-keys.rst,
etc.
As -1 is reserved for static key that's in process of being enabled,
functions would break with negative key->enabled refcount:
- for CONFIG_JUMP_LABEL=n negative return of static_key_count()
breaks static_key_false(), static_key_true()
- the ref counter may become 0 from negative side by too many
static_key_slow_inc() calls and lead to use-after-free issues.
These flaws result in that some users have to introduce an additional
mutex and prevent the reference counter from overflowing themselves,
see bpf_enable_runtime_stats() checking the counter against INT_MAX / 2.
Prevent the reference counter overflow by checking if (v + 1) > 0.
Change functions API to return whether the increment was successful.
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
eb8c507296