linux-kernel - Re: [PATCH] bpf, libbpf: Smatch: Fix potential NULL pointer dereference

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Message-ID: <54a834d7-6adc-c0ad-92aa-1b89e8ada79d@fb.com>
Date:   Tue, 2 Jul 2019 15:34:26 +0000
From:   Yonghong Song <yhs@...com>
To:     Leo Yan <leo.yan@...aro.org>, Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] bpf, libbpf: Smatch: Fix potential NULL pointer
 dereference



On 7/2/19 3:25 AM, Leo Yan wrote:
> Based on the following report from Smatch, fix the potential
> NULL pointer dereference check.
> 
>    tools/lib/bpf/libbpf.c:3493
>    bpf_prog_load_xattr() warn: variable dereferenced before check 'attr'
>    (see line 3483)
> 
> 3479 int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
> 3480                         struct bpf_object **pobj, int *prog_fd)
> 3481 {
> 3482         struct bpf_object_open_attr open_attr = {
> 3483                 .file           = attr->file,
> 3484                 .prog_type      = attr->prog_type,
>                                         ^^^^^^
> 3485         };
> 
> At the head of function, it directly access 'attr' without checking if
> it's NULL pointer.  This patch moves the values assignment after
> validating 'attr' and 'attr->file'.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Acked-by: Yonghong Song <yhs@...com>