bpf: Validate node_id in arena_alloc_pages()

arena_alloc_pages() accepts a plain int node_id and forwards it through
the entire allocation chain without any bounds checking.

Validate node_id before passing it down the allocation chain in
arena_alloc_pages().

Fixes: 317460317a ("bpf: Introduce bpf_arena.")
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260417152135.1383754-1-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/arena.c

@@ -562,6 +562,10 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
 	u32 uaddr32;
 	int ret, i;
 
+	if (node_id != NUMA_NO_NODE &&
+	    ((unsigned int)node_id >= nr_node_ids || !node_online(node_id)))
+		return 0;
+
 	if (page_cnt > page_cnt_max)
 		return 0;