bpftool: Only set obj->skeleton on complete success

After `bpftool gen skeleton`, the ${bpf_app}.skel.h will provide that
${bpf_app_name}__open helper to load bpf. If there is some error
like ENOMEM, the ${bpf_app_name}__open will rollback(free) the allocated
object, including `bpf_object_skeleton`.

Since the ${bpf_app_name}__create_skeleton set the obj->skeleton first
and not rollback it when error, it will cause double-free in
${bpf_app_name}__destory at ${bpf_app_name}__open. Therefore, we should
set the obj->skeleton before return 0;

Fixes: 5dc7a8b21144 ("bpftool, selftests/bpf: Embed object file inside skeleton")
Signed-off-by: Wei Fu <fuweid89@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220108084008.1053111-1-fuweid89@gmail.com

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index b4695df2ea3d7db8a94f606f41ee884a5e76357f..a7387c265e3cfa3ec1329d893a4aff21352501dd 100644 (file)
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -927,7 +927,6 @@ static int do_skeleton(int argc, char **argv)
                        s = (struct bpf_object_skeleton *)calloc(1, sizeof(*s));\n\
                        if (!s)                                             \n\
                                goto err;                                   \n\
-                       obj->skeleton = s;                                  \n\
                                                                            \n\
                        s->sz = sizeof(*s);                                 \n\
                        s->name = \"%1$s\";                                 \n\
@@ -1000,6 +999,7 @@ static int do_skeleton(int argc, char **argv)
                                                                            \n\
                        s->data = (void *)%2$s__elf_bytes(&s->data_sz);     \n\
                                                                            \n\
+                       obj->skeleton = s;                                  \n\
                        return 0;                                           \n\
                err:                                                        \n\
                        bpf_object__destroy_skeleton(s);                    \n\