bpf: Factor out bpf_link_by_id() helper.

Refactor the code a bit to extract bpf_link_by_id() helper.
It's similar to existing bpf_prog_by_id().

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200819042759.51280-2-alexei.starovoitov@gmail.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 55f694b..a9b7185 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1358,6 +1358,7 @@ int btf_check_type_match(struct bpf_verifier_env *env, struct bpf_prog *prog,
                         struct btf *btf, const struct btf_type *t);
 
 struct bpf_prog *bpf_prog_by_id(u32 id);
+struct bpf_link *bpf_link_by_id(u32 id);
 
 const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id);
 #else /* !CONFIG_BPF_SYSCALL */

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 86299a2..689d736 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4014,40 +4014,50 @@ static int link_detach(union bpf_attr *attr)
        return ret;
 }
 
-static int bpf_link_inc_not_zero(struct bpf_link *link)
+static struct bpf_link *bpf_link_inc_not_zero(struct bpf_link *link)
 {
-       return atomic64_fetch_add_unless(&link->refcnt, 1, 0) ? 0 : -ENOENT;
+       return atomic64_fetch_add_unless(&link->refcnt, 1, 0) ? link : ERR_PTR(-ENOENT);
 }
 
-#define BPF_LINK_GET_FD_BY_ID_LAST_FIELD link_id
-
-static int bpf_link_get_fd_by_id(const union bpf_attr *attr)
+struct bpf_link *bpf_link_by_id(u32 id)
 {
        struct bpf_link *link;
-       u32 id = attr->link_id;
-       int fd, err;
 
-       if (CHECK_ATTR(BPF_LINK_GET_FD_BY_ID))
-               return -EINVAL;
-
-       if (!capable(CAP_SYS_ADMIN))
-               return -EPERM;
+       if (!id)
+               return ERR_PTR(-ENOENT);
 
        spin_lock_bh(&link_idr_lock);
-       link = idr_find(&link_idr, id);
        /* before link is "settled", ID is 0, pretend it doesn't exist yet */
+       link = idr_find(&link_idr, id);
        if (link) {
                if (link->id)
-                       err = bpf_link_inc_not_zero(link);
+                       link = bpf_link_inc_not_zero(link);
                else
-                       err = -EAGAIN;
+                       link = ERR_PTR(-EAGAIN);
        } else {
-               err = -ENOENT;
+               link = ERR_PTR(-ENOENT);
        }
        spin_unlock_bh(&link_idr_lock);
+       return link;
+}
 
-       if (err)
-               return err;
+#define BPF_LINK_GET_FD_BY_ID_LAST_FIELD link_id
+
+static int bpf_link_get_fd_by_id(const union bpf_attr *attr)
+{
+       struct bpf_link *link;
+       u32 id = attr->link_id;
+       int fd;
+
+       if (CHECK_ATTR(BPF_LINK_GET_FD_BY_ID))
+               return -EINVAL;
+
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
+       link = bpf_link_by_id(id);
+       if (IS_ERR(link))
+               return PTR_ERR(link);
 
        fd = bpf_link_new_fd(link);
        if (fd < 0)