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>
Link: https://lore.kernel.org/r/20250730234733.530041-1-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f9cd2164ed238d19f0d07ce15f3134add9346e66..308530c8326bf866447eda1a697706c4e9f53540 100644 (file)
--- 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 e63039817af38b3e610bf1cb16c1e4735f423cb7..7a814e98d5f5cf14105afa62ac0f4179dbaca890 100644 (file)
--- 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);