bpf: make direct packet write unclone more robust

Given this seems to be quite fragile and can easily slip through the
cracks, lets make direct packet write more robust by requiring that
future program types which allow for such write must provide a prologue
callback. In case of XDP and sk_msg it's noop, thus add a generic noop
handler there. The latter starts out with NULL data/data_end unconditionally
when sg pages are shared.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5fc9a658af0e1ddc270590ea153fe0395617ae19..171a2c88e77ddd28ea5f9d5ba135d424cd09714e 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5709,7 +5709,11 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
        bool is_narrower_load;
        u32 target_size;
 
-       if (ops->gen_prologue) {
+       if (ops->gen_prologue || env->seen_direct_write) {
+               if (!ops->gen_prologue) {
+                       verbose(env, "bpf verifier is misconfigured\n");
+                       return -EINVAL;
+               }
                cnt = ops->gen_prologue(insn_buf, env->seen_direct_write,
                                        env->prog);
                if (cnt >= ARRAY_SIZE(insn_buf)) {

diff --git a/net/core/filter.c b/net/core/filter.c
index 3fdddfa9a0fd983cf400b3cf5ebca6426b1e377c..cd648d09a8e5b01c2759549942f15f208a39b2d8 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5644,6 +5644,15 @@ static bool sock_filter_is_valid_access(int off, int size,
                                               prog->expected_attach_type);
 }
 
+static int bpf_noop_prologue(struct bpf_insn *insn_buf, bool direct_write,
+                            const struct bpf_prog *prog)
+{
+       /* Neither direct read nor direct write requires any preliminary
+        * action.
+        */
+       return 0;
+}
+
 static int bpf_unclone_prologue(struct bpf_insn *insn_buf, bool direct_write,
                                const struct bpf_prog *prog, int drop_verdict)
 {
@@ -7210,6 +7219,7 @@ const struct bpf_verifier_ops xdp_verifier_ops = {
        .get_func_proto         = xdp_func_proto,
        .is_valid_access        = xdp_is_valid_access,
        .convert_ctx_access     = xdp_convert_ctx_access,
+       .gen_prologue           = bpf_noop_prologue,
 };
 
 const struct bpf_prog_ops xdp_prog_ops = {
@@ -7308,6 +7318,7 @@ const struct bpf_verifier_ops sk_msg_verifier_ops = {
        .get_func_proto         = sk_msg_func_proto,
        .is_valid_access        = sk_msg_is_valid_access,
        .convert_ctx_access     = sk_msg_convert_ctx_access,
+       .gen_prologue           = bpf_noop_prologue,
 };
 
 const struct bpf_prog_ops sk_msg_prog_ops = {