[PATCH bpf-next v3 2/7] bpf/syscall: allow key to be null in map functions

Mauricio Vasquez B
2018-10-18T21:17:38Z

This commit adds the required logic to allow key being NULL
in case the key_size of the map is 0.

A new __bpf_copy_key function helper only copies the key from
userpsace when key_size != 0, otherwise it enforces that key must be
null.

Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>
Acked-by: Song Liu <songliubraving@fb.com>
---
kernel/bpf/syscall.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f4ecd6ed2252..78d9dd95e25f 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -651,6 +651,17 @@ int __weak bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
return -ENOTSUPP;
}

+static void *__bpf_copy_key(void __user *ukey, u64 key_size)
+{
+ if (key_size)
+ return memdup_user(ukey, key_size);
+
+ if (ukey)
+ return ERR_PTR(-EINVAL);
+
+ return NULL;
+}
+
/* last field in 'union bpf_attr' used by this command */
#define BPF_MAP_LOOKUP_ELEM_LAST_FIELD value

@@ -678,7 +689,7 @@ static int map_lookup_elem(union bpf_attr *attr)
goto err_put;
}

- key = memdup_user(ukey, map->key_size);
+ key = __bpf_copy_key(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
goto err_put;
@@ -785,7 +796,7 @@ static int map_update_elem(union bpf_attr *attr)
goto err_put;
}

- key = memdup_user(ukey, map->key_size);
+ key = __bpf_copy_key(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
goto err_put;
@@ -888,7 +899,7 @@ static int map_delete_elem(union bpf_attr *attr)
goto err_put;
}

- key = memdup_user(ukey, map->key_size);
+ key = __bpf_copy_key(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
goto err_put;
@@ -941,7 +952,7 @@ static int map_get_next_key(union bpf_attr *attr)
}

if (ukey) {
- key = memdup_user(ukey, map->key_size);
+ key = __bpf_copy_key(ukey, map->key_size);
if (IS_ERR(key)) {
err = PTR_ERR(key);
goto err_put;