netdev - Re: [PATCH v3 bpf]: libbpf: fixing leak when kernel does not support btf

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Message-ID: <20190308164524.esibgk5yd7a5vq2o@kafai-mbp.dhcp.thefacebook.com>
Date:   Fri, 8 Mar 2019 16:45:27 +0000
From:   Martin Lau <kafai@...com>
To:     "Nikita V. Shirokov" <tehnerd@...nerd.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 bpf]: libbpf: fixing leak when kernel does not support
 btf

On Fri, Mar 08, 2019 at 05:18:14AM +0000, Nikita V. Shirokov wrote:
> we could end up in situation when we have object file w/ all btf
> info but kernel does not support btf yet. in this situation currently
> libbpf just set obj->btf to NULL w/o freeing it first.
> this patch if fixing it by making sure to run btf__free first
> 
> v2->v3:
>  - adding "Fixes" tag
> 
> v1->v2:
>  - adding netdev to cc
> 
> Fixes: 8a138aed4a80 ("bpf: btf: Add BTF support to libbpf")
I think the Fixes tag should belong to a later patch, just in
case there will be an issue when pulling into stable:

Fixes: d29d87f7e612 ("btf: separate btf creation and loading")

> Signed-off-by: Nikita V. Shirokov <tehnerd@...nerd.com>
> ---
>  tools/lib/bpf/libbpf.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index f5eb60379c8d..d5b830d60601 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -838,6 +838,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
>  			if (IS_ERR(obj->btf) || btf__load(obj->btf)) {
>  				pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
>  					   BTF_ELF_SEC, PTR_ERR(obj->btf));
Printing this PTR_ERR(obj->btf) seems not very correct also if btf__load()
was the one failing.

> +				if (!IS_ERR(obj->btf))
> +					btf__free(obj->btf);
>  				obj->btf = NULL;
>  			}
>  		} else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
> -- 
> 2.17.1
>