linux-kernel - RE: [PATCH] [bpf] xdp_monitor_user: Fix null pointer dereference

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Date:   Tue, 16 Jun 2020 00:05:58 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Gaurav Singh <gaurav1086@...il.com>, gaurav1086@...il.com,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "(open list:BPF \\(Safe dynamic programs and tools\\))" 
        <netdev@...r.kernel.org>,
        bpf@...r.kernel.org (open list:BPF \(Safe dynamic programs and tools\)),
        "(open list:BPF \\(Safe dynamic programs and tools\\) open list)" 
        <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] [bpf] xdp_monitor_user: Fix null pointer dereference

Gaurav Singh wrote:
> Memset() on the pointer right after malloc() can cause
> a null pointer dereference if it failed to allocate memory.
> Fix this by replacing malloc/memset with a single calloc().
> 
> Signed-off-by: Gaurav Singh <gaurav1086@...il.com>
> ---
>  samples/bpf/xdp_monitor_user.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/samples/bpf/xdp_monitor_user.c b/samples/bpf/xdp_monitor_user.c
> index dd558cbb2309..ef53b93db573 100644
> --- a/samples/bpf/xdp_monitor_user.c
> +++ b/samples/bpf/xdp_monitor_user.c
> @@ -509,11 +509,8 @@ static void *alloc_rec_per_cpu(int record_size)
>  {
>  	unsigned int nr_cpus = bpf_num_possible_cpus();
>  	void *array;
> -	size_t size;
>  
> -	size = record_size * nr_cpus;
> -	array = malloc(size);
> -	memset(array, 0, size);
> +	array = calloc(nr_cpus, record_size);
>  	if (!array) {
>  		fprintf(stderr, "Mem alloc error (nr_cpus:%u)\n", nr_cpus);
>  		exit(EXIT_FAIL_MEM);
> @@ -528,8 +525,7 @@ static struct stats_record *alloc_stats_record(void)
>  	int i;
>  
>  	/* Alloc main stats_record structure */
> -	rec = malloc(sizeof(*rec));
> -	memset(rec, 0, sizeof(*rec));
> +	rec = calloc(1, sizeof(*rec));
>  	if (!rec) {
>  		fprintf(stderr, "Mem alloc error\n");
>  		exit(EXIT_FAIL_MEM);
> -- 
> 2.17.1
> 

Acked-by: John Fastabend <john.fastabend@...il.com>