bpf: Limit the number of kprobes when attaching program to multiple kprobes

An abnormally big cnt may also be assigned to kprobe_multi.cnt when
attaching multiple kprobes. It will trigger the following warning in
kvmalloc_node():

	if (unlikely(size > INT_MAX)) {
	    WARN_ON_ONCE(!(flags & __GFP_NOWARN));
	    return NULL;
	}

Fix the warning by limiting the maximal number of kprobes in
bpf_kprobe_multi_link_attach(). If the number of kprobes is greater than
MAX_KPROBE_MULTI_CNT, the attachment will fail and return -E2BIG.

Fixes: 0dcac27 ("bpf: Add multi kprobe link")
Signed-off-by: Hou Tao <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: Hou Tao

kernel/trace/bpf_trace.c

@@ -43,6 +43,7 @@
 	rcu_dereference_protected(p, lockdep_is_held(&bpf_event_mutex))
 
 #define MAX_UPROBE_MULTI_CNT (1U << 20)
+#define MAX_KPROBE_MULTI_CNT (1U << 20)
 
 #ifdef CONFIG_MODULES
 struct bpf_trace_module {
@@ -2972,6 +2973,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	cnt = attr->link_create.kprobe_multi.cnt;
 	if (!cnt)
 		return -EINVAL;
+	if (cnt > MAX_KPROBE_MULTI_CNT)
+		return -E2BIG;
 
 	size = cnt * sizeof(*addrs);
 	addrs = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);