bpf: Clear per_cpu pointers during bpf_prog_realloc

bpf_prog_realloc copies contents of struct bpf_prog.
The pointers have to be cleared before freeing old struct.

Reported-by: Ilya Leoshkevich <iii@linux.ibm.com>
Fixes: 700d479 ("bpf: Optimize program stats")
Fixes: ca06f55 ("bpf: Add per-program recursion prevention mechanism")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/core.c

@@ -245,6 +245,8 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
 		 * reallocated structure.
 		 */
 		fp_old->aux = NULL;
+		fp_old->stats = NULL;
+		fp_old->active = NULL;
 		__bpf_prog_free(fp_old);
 	}