bpf: Dont allow vmlinux BTF to be used in map_create and prog_load.

The syzbot got FD of vmlinux BTF and passed it into map_create which caused
crash in btf_type_id_size() when it tried to access resolved_ids. The vmlinux
BTF doesn't have 'resolved_ids' and 'resolved_sizes' initialized to save
memory. To avoid such issues disallow using vmlinux BTF in prog_load and
map_create commands.

Fixes: 5329722057d4 ("bpf: Assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ_INFO")
Reported-by: syzbot+8bab8ed346746e7540e8@syzkaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210307225248.79031-1-alexei.starovoitov@gmail.com

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c859bc4..2505034 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -854,6 +854,11 @@ static int map_create(union bpf_attr *attr)
                        err = PTR_ERR(btf);
                        goto free_map;
                }
+               if (btf_is_kernel(btf)) {
+                       btf_put(btf);
+                       err = -EACCES;
+                       goto free_map;
+               }
                map->btf = btf;
 
                if (attr->btf_value_type_id) {

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c56e3fc..4192a9e 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9056,6 +9056,10 @@ static int check_btf_info(struct bpf_verifier_env *env,
        btf = btf_get_by_fd(attr->prog_btf_fd);
        if (IS_ERR(btf))
                return PTR_ERR(btf);
+       if (btf_is_kernel(btf)) {
+               btf_put(btf);
+               return -EACCES;
+       }
        env->prog->aux->btf = btf;
 
        err = check_btf_func(env, attr, uattr);