bpf: Drop redundant hash_buf from map_get_hash operation

bpf_map_get_info_by_fd() is the only caller of the ->map_get_hash
and always invokes it with hash_buf == map->sha and hash_buf_size
of SHA256_DIGEST_SIZE. array_map_get_hash() in turn lets sha256()
write the digest directly into that buffer (map->sha) and then
performs a trailing memcpy(), which evaluates to memcpy(map->sha,
map->sha, 32): a redundant self-copy. The hash_buf_size argument
was never used at all. Simplify this a bit, no functional change.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260601150248.394863-3-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: borkmann

include/linux/bpf.h

@@ -111,7 +111,7 @@ struct bpf_map_ops {
 	long (*map_pop_elem)(struct bpf_map *map, void *value);
 	long (*map_peek_elem)(struct bpf_map *map, void *value);
 	void *(*map_lookup_percpu_elem)(struct bpf_map *map, void *key, u32 cpu);
-	int (*map_get_hash)(struct bpf_map *map, u32 hash_buf_size, void *hash_buf);
+	int (*map_get_hash)(struct bpf_map *map);
 
 	/* funcs called by prog_array and perf_event_array map */
 	void *(*map_fd_get_ptr)(struct bpf_map *map, struct file *map_file,

kernel/bpf/arraymap.c

@@ -175,14 +175,12 @@ static void *array_map_lookup_elem(struct bpf_map *map, void *key)
 	return array->value + (u64)array->elem_size * (index & array->index_mask);
 }
 
-static int array_map_get_hash(struct bpf_map *map, u32 hash_buf_size,
-			       void *hash_buf)
+static int array_map_get_hash(struct bpf_map *map)
 {
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 
 	sha256(array->value, (u64)array->elem_size * array->map.max_entries,
-	       hash_buf);
-	memcpy(array->map.sha, hash_buf, sizeof(array->map.sha));
+	       array->map.sha);
 	return 0;
 }
 

kernel/bpf/syscall.c

@@ -5434,18 +5434,16 @@ static int bpf_map_get_info_by_fd(struct file *file,
 
 		if (!map->ops->map_get_hash)
 			return -EINVAL;
-
-		if (info.hash_size != SHA256_DIGEST_SIZE)
+		if (info.hash_size != sizeof(map->sha))
 			return -EINVAL;
-
 		if (!READ_ONCE(map->frozen))
 			return -EPERM;
 
-		err = map->ops->map_get_hash(map, SHA256_DIGEST_SIZE, map->sha);
+		err = map->ops->map_get_hash(map);
 		if (err != 0)
 			return err;
 
-		if (copy_to_user(uhash, map->sha, SHA256_DIGEST_SIZE) != 0)
+		if (copy_to_user(uhash, map->sha, sizeof(map->sha)) != 0)
 			return -EFAULT;
 	} else if (info.hash_size) {
 		return -EINVAL;