bpf: don't zero out the info struct in bpf_obj_get_info_by_fd()

The buffer passed to bpf_obj_get_info_by_fd() should be initialized
to zeros.  Kernel will enforce that to guarantee we can safely extend
info structures in the future.

Making the bpf_obj_get_info_by_fd() call in libbpf perform the zeroing
is problematic, however, since some members of the info structures
may need to be initialized by the callers (for instance pointers
to buffers to which kernel is to dump translated and jited images).

Remove the zeroing and fix up the in-tree callers before any kernel
has been released with this code.

As Daniel points out this seems to be the intended operation anyway,
since commit 95b9afd398 ("bpf: Test for bpf ID") is itself setting
the buffer pointers before calling bpf_obj_get_info_by_fd().

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/lib/bpf/bpf.c

@@ -314,7 +314,6 @@ int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len)
 	int err;
 
 	bzero(&attr, sizeof(attr));
-	bzero(info, *info_len);
 	attr.info.bpf_fd = prog_fd;
 	attr.info.info_len = *info_len;
 	attr.info.info = ptr_to_u64(info);

tools/testing/selftests/bpf/test_progs.c

@@ -340,6 +340,7 @@ static void test_bpf_obj_id(void)
 
 		/* Check getting prog info */
 		info_len = sizeof(struct bpf_prog_info) * 2;
+		bzero(&prog_infos[i], info_len);
 		prog_infos[i].jited_prog_insns = ptr_to_u64(jited_insns);
 		prog_infos[i].jited_prog_len = sizeof(jited_insns);
 		prog_infos[i].xlated_prog_insns = ptr_to_u64(xlated_insns);
@@ -369,6 +370,7 @@ static void test_bpf_obj_id(void)
 
 		/* Check getting map info */
 		info_len = sizeof(struct bpf_map_info) * 2;
+		bzero(&map_infos[i], info_len);
 		err = bpf_obj_get_info_by_fd(map_fds[i], &map_infos[i],
 					     &info_len);
 		if (CHECK(err ||
@@ -394,7 +396,7 @@ static void test_bpf_obj_id(void)
 	nr_id_found = 0;
 	next_id = 0;
 	while (!bpf_prog_get_next_id(next_id, &next_id)) {
-		struct bpf_prog_info prog_info;
+		struct bpf_prog_info prog_info = {};
 		int prog_fd;
 
 		info_len = sizeof(prog_info);
@@ -418,6 +420,8 @@ static void test_bpf_obj_id(void)
 		nr_id_found++;
 
 		err = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &info_len);
+		prog_infos[i].jited_prog_insns = 0;
+		prog_infos[i].xlated_prog_insns = 0;
 		CHECK(err || info_len != sizeof(struct bpf_prog_info) ||
 		      memcmp(&prog_info, &prog_infos[i], info_len),
 		      "get-prog-info(next_id->fd)",
@@ -436,7 +440,7 @@ static void test_bpf_obj_id(void)
 	nr_id_found = 0;
 	next_id = 0;
 	while (!bpf_map_get_next_id(next_id, &next_id)) {
-		struct bpf_map_info map_info;
+		struct bpf_map_info map_info = {};
 		int map_fd;
 
 		info_len = sizeof(map_info);