From: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Date: Thu, 13 Nov 2014 17:36:49 -0800
> +static u64 bpf_map_lookup_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
> +{
> + /* verifier checked that R1 contains a valid pointer to bpf_map
> + * and R2 points to a program stack and map->key_size bytes were
> + * initialized
> + */
> + struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
> + void *key = (void *) (unsigned long) r2;
> + void *value;
> +
> + WARN_ON_ONCE(!rcu_read_lock_held());
> +
> + value = map->ops->map_lookup_elem(map, key);
> +
> + /* lookup() returns either pointer to element value or NULL
> + * which is the meaning of PTR_TO_MAP_VALUE_OR_NULL type
> + */
> + return (unsigned long) value;
> +}
You should translate this into a true boolean '1' or '0' value so that
kernel pointers don't propagate to the user or his eBPF programs.
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