Re: [PATCH] bpftool: check for NULL ptr of btf in codegen_subskel_datasecs

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On 8/21/24 6:31 AM, Ma Ke wrote:
bpf_object__btf() can return NULL value.  If bpf_object__btf returns null,
do not progress through codegen_subskel_datasecs(). This avoids a null ptr
dereference.

Found by code review, complie tested only.

Do you have a real case to show null ptr reference here?
Code review and compile test are not enough. You should have
a real reproducible case before you send the patch.

For this particular case, we have check

        btf = bpf_object__btf(obj);
        if (!btf) {
                err = -1;
                p_err("need btf type information for %s", obj_name);
                goto out;
        }

which ensures that btf is available before codegen for subskeleton,
so what you described won't happen in practice.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 00389c58ffe9 ("bpftool: Add support for subskeletons")
Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>
---
  tools/bpf/bpftool/gen.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 5a4d3240689e..7ce62f280310 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -334,6 +334,9 @@ static int codegen_subskel_datasecs(struct bpf_object *obj, const char *obj_name
  	const char *sec_name, *var_name;
  	__u32 var_type_id;
+ if (!btf)
+		return -EINVAL;
+
  	d = btf_dump__new(btf, codegen_btf_dump_printf, NULL, NULL);
  	if (!d)
  		return -errno;




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