bpf: respect size hint to BPF_PROG_TEST_RUN if present

Use data_size_out as a size hint when copying test output to user space.
ENOSPC is returned if the output buffer is too small.
Callers which so far did not set data_size_out are not affected.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c89c22c49015..7663e6a57280 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -74,8 +74,18 @@ static int bpf_test_finish(const union bpf_attr *kattr,
 {
         void __user *data_out = u64_to_user_ptr(kattr->test.data_out);
         int err = -EFAULT;
+        u32 copy_size = size;
+
+        /* Clamp copy if the user has provided a size hint, but copy the full
+         * buffer if not to retain old behaviour.
+         */
+        if (kattr->test.data_size_out &&
+            copy_size > kattr->test.data_size_out) {
+                copy_size = kattr->test.data_size_out;
+                err = -ENOSPC;
+        }
 
-        if (data_out && copy_to_user(data_out, data, size))
+        if (data_out && copy_to_user(data_out, data, copy_size))
                 goto out;
         if (copy_to_user(&uattr->test.data_size_out, &size, sizeof(size)))
                 goto out;
@@ -83,7 +93,8 @@ static int bpf_test_finish(const union bpf_attr *kattr,
                 goto out;
         if (copy_to_user(&uattr->test.duration, &duration, sizeof(duration)))
                 goto out;
-        err = 0;
+        if (err != -ENOSPC)
+                err = 0;
 out:
         return err;
 }