selftest/bpf: Check invalid length in test_xdp_update_frags

Update test_xdp_update_frags adding a test for a buffer size
set to (MAX_SKB_FRAGS + 2) * PAGE_SIZE. The kernel is supposed
to return -ENOMEM.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/3e4afa0ee4976854b2f0296998fe6754a80b62e5.1644366736.git.lorenzo@kernel.org

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_adjust_frags.c b/tools/testing/selftests/bpf/prog_tests/xdp_adjust_frags.c
index d18e6f3..2f033da 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/xdp_adjust_frags.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_adjust_frags.c
@@ -5,11 +5,12 @@
 static void test_xdp_update_frags(void)
 {
        const char *file = "./test_xdp_update_frags.o";
+       int err, prog_fd, max_skb_frags, buf_size, num;
        struct bpf_program *prog;
        struct bpf_object *obj;
-       int err, prog_fd;
        __u32 *offset;
        __u8 *buf;
+       FILE *f;
        LIBBPF_OPTS(bpf_test_run_opts, topts);
 
        obj = bpf_object__open(file);
@@ -99,6 +100,41 @@ static void test_xdp_update_frags(void)
        ASSERT_EQ(buf[7621], 0xbb, "xdp_update_frag buf[7621]");
 
        free(buf);
+
+       /* test_xdp_update_frags: unsupported buffer size */
+       f = fopen("/proc/sys/net/core/max_skb_frags", "r");
+       if (!ASSERT_OK_PTR(f, "max_skb_frag file pointer"))
+               goto out;
+
+       num = fscanf(f, "%d", &max_skb_frags);
+       fclose(f);
+
+       if (!ASSERT_EQ(num, 1, "max_skb_frags read failed"))
+               goto out;
+
+       /* xdp_buff linear area size is always set to 4096 in the
+        * bpf_prog_test_run_xdp routine.
+        */
+       buf_size = 4096 + (max_skb_frags + 1) * sysconf(_SC_PAGE_SIZE);
+       buf = malloc(buf_size);
+       if (!ASSERT_OK_PTR(buf, "alloc buf"))
+               goto out;
+
+       memset(buf, 0, buf_size);
+       offset = (__u32 *)buf;
+       *offset = 16;
+       buf[*offset] = 0xaa;
+       buf[*offset + 15] = 0xaa;
+
+       topts.data_in = buf;
+       topts.data_out = buf;
+       topts.data_size_in = buf_size;
+       topts.data_size_out = buf_size;
+
+       err = bpf_prog_test_run_opts(prog_fd, &topts);
+       ASSERT_EQ(err, -ENOMEM,
+                 "unsupported buf size, possible non-default /proc/sys/net/core/max_skb_flags?");
+       free(buf);
 out:
        bpf_object__close(obj);
 }