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

An abnormally big cnt may be passed to link_create.uprobe_multi.cnt,
and 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 uprobes in
bpf_uprobe_multi_link_attach(). If the number of uprobes is greater than
MAX_UPROBE_MULTI_CNT, the attachment will return -E2BIG.

Fixes: 89ae89f ("bpf: Add multi uprobe link")
Reported-by: Xingwei Lee <[email protected]>
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]>
Closes: https://lore.kernel.org/bpf/CABOYnLwwJY=yFAGie59LFsUsBAgHfroVqbzZ5edAXbFE3YiNVA@mail.gmail.com
Link: https://lore.kernel.org/bpf/[email protected]

Author: Hou Tao

kernel/trace/bpf_trace.c

@@ -42,6 +42,8 @@
 #define bpf_event_rcu_dereference(p)					\
 	rcu_dereference_protected(p, lockdep_is_held(&bpf_event_mutex))
 
+#define MAX_UPROBE_MULTI_CNT (1U << 20)
+
 #ifdef CONFIG_MODULES
 struct bpf_trace_module {
 	struct module *module;
@@ -3344,6 +3346,8 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 
 	if (!upath || !uoffsets || !cnt)
 		return -EINVAL;
+	if (cnt > MAX_UPROBE_MULTI_CNT)
+		return -E2BIG;
 
 	uref_ctr_offsets = u64_to_user_ptr(attr->link_create.uprobe_multi.ref_ctr_offsets);
 	ucookies = u64_to_user_ptr(attr->link_create.uprobe_multi.cookies);