Re: [PATCH dwarves] btf_encoder: always initialize func_state to 0

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Jan 10, 2025 at 02:31:41AM +0000, Ihor Solodrai wrote:
> BPF CI caught a segfault on aarch64 and s390x [1] after recent merges
> into the master branch.

In the past the libbpf github actions was tracking the tmp.master (it would
be better to track "next") branch and I was looking at when it passed to
then move "next" to master, that would be great to have so that we
wouldn't be having these bugs in the git history, avoiding force pushes.

Anyhway, thanks for the fix, I'll add it and push it out.

- Arnaldo
 
> The segfault happened at free(func_state->annots) in
> btf_encoder__delete_saved_funcs().
> 
> func_state->annots arrived there uninitialized because after patch [2]
> in some cases func_state may be allocated with a realloc, but was not
> zeroed out.
> 
> Fix this bug by always memset-ing a func_state to zero in
> btf_encoder__alloc_func_state().
> 
> [1] https://github.com/kernel-patches/bpf/actions/runs/12700574327
> [2] https://lore.kernel.org/dwarves/20250109185950.653110-11-ihor.solodrai@pm.me/
> ---
>  btf_encoder.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 78efd70..511c1ea 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -1083,7 +1083,7 @@ static bool funcs__match(struct btf_encoder_func_state *s1,
>  
>  static struct btf_encoder_func_state *btf_encoder__alloc_func_state(struct btf_encoder *encoder)
>  {
> -	struct btf_encoder_func_state *tmp;
> +	struct btf_encoder_func_state *state, *tmp;
>  
>  	if (encoder->func_states.cnt >= encoder->func_states.cap) {
>  
> @@ -1100,7 +1100,10 @@ static struct btf_encoder_func_state *btf_encoder__alloc_func_state(struct btf_e
>  		encoder->func_states.array = tmp;
>  	}
>  
> -	return &encoder->func_states.array[encoder->func_states.cnt++];
> +	state = &encoder->func_states.array[encoder->func_states.cnt++];
> +	memset(state, 0, sizeof(*state));
> +
> +	return state;
>  }
>  
>  static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct function *fn, struct elf_function *func)
> -- 
> 2.47.1
>