bpf: Add cookie object to bpf maps

Add a cookie to BPF maps to uniquely identify BPF maps for the timespan
when the node is up. This is different to comparing a pointer or BPF map
id which could get rolled over and reused.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/bpf.h  | 1 +
 kernel/bpf/syscall.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f9cd2164ed23..308530c8326b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -310,6 +310,7 @@ struct bpf_map {
 	bool free_after_rcu_gp;
 	atomic64_t sleepable_refcnt;
 	s64 __percpu *elem_count;
+	u64 cookie; /* write-once */
 };
 
 static inline const char *btf_field_type_name(enum btf_field_type type)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e63039817af3..7a814e98d5f5 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -37,6 +37,7 @@
 #include <linux/trace_events.h>
 #include <linux/tracepoint.h>
 #include <linux/overflow.h>
+#include <linux/cookie.h>
 
 #include <net/netfilter/nf_bpf_link.h>
 #include <net/netkit.h>
@@ -53,6 +54,7 @@
 #define BPF_OBJ_FLAG_MASK   (BPF_F_RDONLY | BPF_F_WRONLY)
 
 DEFINE_PER_CPU(int, bpf_prog_active);
+DEFINE_COOKIE(bpf_map_cookie);
 static DEFINE_IDR(prog_idr);
 static DEFINE_SPINLOCK(prog_idr_lock);
 static DEFINE_IDR(map_idr);
@@ -1487,6 +1489,10 @@ static int map_create(union bpf_attr *attr, bool kernel)
 	if (err < 0)
 		goto free_map;
 
+	preempt_disable();
+	map->cookie = gen_cookie_next(&bpf_map_cookie);
+	preempt_enable();
+
 	atomic64_set(&map->refcnt, 1);
 	atomic64_set(&map->usercnt, 1);
 	mutex_init(&map->freeze_mutex);
-- 
2.43.0