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jump_label: Prevent key->enabled int overflow
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 <[email protected]> Acked-by: Jakub Kicinski <[email protected]> Acked-by: Peter Zijlstra (Intel) <[email protected]> Signed-off-by: Jakub Kicinski <[email protected]>
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