[PATCH umdns] service.c: fix build on gcc 10

[Kevin Darbyshire-Bryant]

Resolve error:
/Users/kevin/wrt/build_dir/target-x86_64_musl/umdns-2020-06-08-d13290b4/service.c: In function 'service_load_blob':
/Users/kevin/wrt/build_dir/target-x86_64_musl/umdns-2020-06-08-d13290b4/service.c:240:10: error: 'strcpy' offset 6 from the object at 'b' is out of the bounds of referenced subobject 'name' with type 'uint8_t[]' {aka 'unsigned char[]'} at offset 6 [-Werror=array-bounds]
  240 |  s->id = strcpy(d_id, blobmsg_name(b));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /Users/kevin/wrt/staging_dir/target-x86_64_musl/usr/include/libubus.h:23,
                 from /Users/kevin/wrt/build_dir/target-x86_64_musl/umdns-2020-06-08-d13290b4/service.c:23:
/Users/kevin/wrt/staging_dir/target-x86_64_musl/usr/include/libubox/blobmsg.h:42:10: note: subobject 'name' declared here
   42 |  uint8_t name[];
      |          ^~~~
cc1: all warnings being treated as errors
make[5]: *** [CMakeFiles/umdns.dir/build.make:132: CMakeFiles/umdns.dir/service.c.o] Error 1

Signed-off-by: Kevin Darbyshire-Bryant <ldir at darbyshire-bryant.me.uk>
---
 service.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/service.c b/service.c
index 97b6f91..af3083e 100644
--- a/service.c
+++ b/service.c
@@ -218,6 +218,7 @@ service_load_blob(struct blob_attr *b)
 	uint8_t *d_txt;
 	int rem2;
 	int txt_len = 0;
+	unsigned int n;
 
 	blobmsg_parse(service_policy, ARRAY_SIZE(service_policy),
 		_tb, blobmsg_data(b), blobmsg_data_len(b));
@@ -228,8 +229,9 @@ service_load_blob(struct blob_attr *b)
 		blobmsg_for_each_attr(txt, _tb[SERVICE_TXT], rem2)
 			txt_len += 1 + strlen(blobmsg_get_string(txt));
 
+	n = strlen(blobmsg_name(b)) + 1;
 	s = calloc_a(sizeof(*s),
-		&d_id, strlen(blobmsg_name(b)) + 1,
+		&d_id, n,
 		&d_instance, _tb[SERVICE_INSTANCE] ? strlen(blobmsg_get_string(_tb[SERVICE_INSTANCE])) + 1 : 0,
 		&d_service, strlen(blobmsg_get_string(_tb[SERVICE_SERVICE])) + 1,
 		&d_txt, txt_len);
@@ -237,7 +239,7 @@ service_load_blob(struct blob_attr *b)
 		return;
 
 	s->port = blobmsg_get_u32(_tb[SERVICE_PORT]);
-	s->id = strcpy(d_id, blobmsg_name(b));
+	s->id = strncpy(d_id, blobmsg_name(b), n);
 	if (_tb[SERVICE_INSTANCE])
 		s->instance = strcpy(d_instance, blobmsg_get_string(_tb[SERVICE_INSTANCE]));
 	else
-- 
2.24.3 (Apple Git-128)