bpf: add lookup/update/delete/iterate methods to BPF maps

'maps' is a generic storage of different types for sharing data between kernel
and userspace.

The maps are accessed from user space via BPF syscall, which has commands:

- create a map with given type and attributes
  fd = bpf(BPF_MAP_CREATE, union bpf_attr *attr, u32 size)
  returns fd or negative error

- lookup key in a given map referenced by fd
  err = bpf(BPF_MAP_LOOKUP_ELEM, union bpf_attr *attr, u32 size)
  using attr->map_fd, attr->key, attr->value
  returns zero and stores found elem into value or negative error

- create or update key/value pair in a given map
  err = bpf(BPF_MAP_UPDATE_ELEM, union bpf_attr *attr, u32 size)
  using attr->map_fd, attr->key, attr->value
  returns zero or negative error

- find and delete element by key in a given map
  err = bpf(BPF_MAP_DELETE_ELEM, union bpf_attr *attr, u32 size)
  using attr->map_fd, attr->key

- iterate map elements (based on input key return next_key)
  err = bpf(BPF_MAP_GET_NEXT_KEY, union bpf_attr *attr, u32 size)
  using attr->map_fd, attr->key, attr->next_key

- close(fd) deletes the map

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 235 insertions, 0 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 428a0e23adc0..f94349ecaf61 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -13,6 +13,7 @@
 #include <linux/syscalls.h>
 #include <linux/slab.h>
 #include <linux/anon_inodes.h>
+#include <linux/file.h>
 
 static LIST_HEAD(bpf_map_types);
 
@@ -111,6 +112,228 @@ free_map:
         return err;
 }
 
+/* if error is returned, fd is released.
+ * On success caller should complete fd access with matching fdput()
+ */
+struct bpf_map *bpf_map_get(struct fd f)
+{
+        struct bpf_map *map;
+
+        if (!f.file)
+                return ERR_PTR(-EBADF);
+
+        if (f.file->f_op != &bpf_map_fops) {
+                fdput(f);
+                return ERR_PTR(-EINVAL);
+        }
+
+        map = f.file->private_data;
+
+        return map;
+}
+
+/* helper to convert user pointers passed inside __aligned_u64 fields */
+static void __user *u64_to_ptr(__u64 val)
+{
+        return (void __user *) (unsigned long) val;
+}
+
+/* last field in 'union bpf_attr' used by this command */
+#define BPF_MAP_LOOKUP_ELEM_LAST_FIELD value
+
+static int map_lookup_elem(union bpf_attr *attr)
+{
+        void __user *ukey = u64_to_ptr(attr->key);
+        void __user *uvalue = u64_to_ptr(attr->value);
+        int ufd = attr->map_fd;
+        struct fd f = fdget(ufd);
+        struct bpf_map *map;
+        void *key, *value;
+        int err;
+
+        if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
+                return -EINVAL;
+
+        map = bpf_map_get(f);
+        if (IS_ERR(map))
+                return PTR_ERR(map);
+
+        err = -ENOMEM;
+        key = kmalloc(map->key_size, GFP_USER);
+        if (!key)
+                goto err_put;
+
+        err = -EFAULT;
+        if (copy_from_user(key, ukey, map->key_size) != 0)
+                goto free_key;
+
+        err = -ESRCH;
+        rcu_read_lock();
+        value = map->ops->map_lookup_elem(map, key);
+        if (!value)
+                goto err_unlock;
+
+        err = -EFAULT;
+        if (copy_to_user(uvalue, value, map->value_size) != 0)
+                goto err_unlock;
+
+        err = 0;
+
+err_unlock:
+        rcu_read_unlock();
+free_key:
+        kfree(key);
+err_put:
+        fdput(f);
+        return err;
+}
+
+#define BPF_MAP_UPDATE_ELEM_LAST_FIELD value
+
+static int map_update_elem(union bpf_attr *attr)
+{
+        void __user *ukey = u64_to_ptr(attr->key);
+        void __user *uvalue = u64_to_ptr(attr->value);
+        int ufd = attr->map_fd;
+        struct fd f = fdget(ufd);
+        struct bpf_map *map;
+        void *key, *value;
+        int err;
+
+        if (CHECK_ATTR(BPF_MAP_UPDATE_ELEM))
+                return -EINVAL;
+
+        map = bpf_map_get(f);
+        if (IS_ERR(map))
+                return PTR_ERR(map);
+
+        err = -ENOMEM;
+        key = kmalloc(map->key_size, GFP_USER);
+        if (!key)
+                goto err_put;
+
+        err = -EFAULT;
+        if (copy_from_user(key, ukey, map->key_size) != 0)
+                goto free_key;
+
+        err = -ENOMEM;
+        value = kmalloc(map->value_size, GFP_USER);
+        if (!value)
+                goto free_key;
+
+        err = -EFAULT;
+        if (copy_from_user(value, uvalue, map->value_size) != 0)
+                goto free_value;
+
+        /* eBPF program that use maps are running under rcu_read_lock(),
+         * therefore all map accessors rely on this fact, so do the same here
+         */
+        rcu_read_lock();
+        err = map->ops->map_update_elem(map, key, value);
+        rcu_read_unlock();
+
+free_value:
+        kfree(value);
+free_key:
+        kfree(key);
+err_put:
+        fdput(f);
+        return err;
+}
+
+#define BPF_MAP_DELETE_ELEM_LAST_FIELD key
+
+static int map_delete_elem(union bpf_attr *attr)
+{
+        void __user *ukey = u64_to_ptr(attr->key);
+        int ufd = attr->map_fd;
+        struct fd f = fdget(ufd);
+        struct bpf_map *map;
+        void *key;
+        int err;
+
+        if (CHECK_ATTR(BPF_MAP_DELETE_ELEM))
+                return -EINVAL;
+
+        map = bpf_map_get(f);
+        if (IS_ERR(map))
+                return PTR_ERR(map);
+
+        err = -ENOMEM;
+        key = kmalloc(map->key_size, GFP_USER);
+        if (!key)
+                goto err_put;
+
+        err = -EFAULT;
+        if (copy_from_user(key, ukey, map->key_size) != 0)
+                goto free_key;
+
+        rcu_read_lock();
+        err = map->ops->map_delete_elem(map, key);
+        rcu_read_unlock();
+
+free_key:
+        kfree(key);
+err_put:
+        fdput(f);
+        return err;
+}
+
+/* last field in 'union bpf_attr' used by this command */
+#define BPF_MAP_GET_NEXT_KEY_LAST_FIELD next_key
+
+static int map_get_next_key(union bpf_attr *attr)
+{
+        void __user *ukey = u64_to_ptr(attr->key);
+        void __user *unext_key = u64_to_ptr(attr->next_key);
+        int ufd = attr->map_fd;
+        struct fd f = fdget(ufd);
+        struct bpf_map *map;
+        void *key, *next_key;
+        int err;
+
+        if (CHECK_ATTR(BPF_MAP_GET_NEXT_KEY))
+                return -EINVAL;
+
+        map = bpf_map_get(f);
+        if (IS_ERR(map))
+                return PTR_ERR(map);
+
+        err = -ENOMEM;
+        key = kmalloc(map->key_size, GFP_USER);
+        if (!key)
+                goto err_put;
+
+        err = -EFAULT;
+        if (copy_from_user(key, ukey, map->key_size) != 0)
+                goto free_key;
+
+        err = -ENOMEM;
+        next_key = kmalloc(map->key_size, GFP_USER);
+        if (!next_key)
+                goto free_key;
+
+        rcu_read_lock();
+        err = map->ops->map_get_next_key(map, key, next_key);
+        rcu_read_unlock();
+        if (err)
+                goto free_next_key;
+
+        err = -EFAULT;
+        if (copy_to_user(unext_key, next_key, map->key_size) != 0)
+                goto free_next_key;
+
+        err = 0;
+
+free_next_key:
+        kfree(next_key);
+free_key:
+        kfree(key);
+err_put:
+        fdput(f);
+        return err;
+}
+
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
         union bpf_attr attr = {};
@@ -160,6 +383,18 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
         case BPF_MAP_CREATE:
                 err = map_create(&attr);
                 break;
+        case BPF_MAP_LOOKUP_ELEM:
+                err = map_lookup_elem(&attr);
+                break;
+        case BPF_MAP_UPDATE_ELEM:
+                err = map_update_elem(&attr);
+                break;
+        case BPF_MAP_DELETE_ELEM:
+                err = map_delete_elem(&attr);
+                break;
+        case BPF_MAP_GET_NEXT_KEY:
+                err = map_get_next_key(&attr);
+                break;
         default:
                 err = -EINVAL;
                 break;