netdev - Re: [PATCH 2/2] samples/bpf: add NULL check for ksym

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Date:   Mon, 25 Mar 2019 12:02:58 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     "Daniel T. Lee" <danieltimlee@...il.com>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] samples/bpf: add NULL check for ksym_search

On 03/15/2019 07:42 AM, Daniel T. Lee wrote:
> Since, ksym_search added with verification logic for symbols existence,
> it could return NULL when the kernel symbols are not loaded.
> 
> This commit will add NULL check logic after ksym_search.
> 
> Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> ---
>  samples/bpf/offwaketime_user.c | 5 +++++
>  samples/bpf/sampleip_user.c    | 5 +++++
>  samples/bpf/trace_event_user.c | 5 +++++
>  3 files changed, 15 insertions(+)

This would also need fixing to check for NULL in:

tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c

> diff --git a/samples/bpf/offwaketime_user.c b/samples/bpf/offwaketime_user.c
> index f06063af9fcb..52e29467a509 100644
> --- a/samples/bpf/offwaketime_user.c
> +++ b/samples/bpf/offwaketime_user.c
> @@ -28,6 +28,11 @@ static void print_ksym(__u64 addr)
>  	if (!addr)
>  		return;
>  	sym = ksym_search(addr);
> +	if (!sym){
> +		printf("ksym not found. Is kallsyms loaded?\n");
> +		return;
> +	}
> +
>  	if (PRINT_RAW_ADDR)
>  		printf("%s/%llx;", sym->name, addr);
>  	else
> diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c
> index 216c7ecbbbe9..23b90a45c802 100644
> --- a/samples/bpf/sampleip_user.c
> +++ b/samples/bpf/sampleip_user.c
> @@ -109,6 +109,11 @@ static void print_ip_map(int fd)
>  	for (i = 0; i < max; i++) {
>  		if (counts[i].ip > PAGE_OFFSET) {
>  			sym = ksym_search(counts[i].ip);
> +			if (!sym) {
> +				printf("ksym not found. Is kallsyms loaded?\n");
> +				continue;
> +			}
> +
>  			printf("0x%-17llx %-32s %u\n", counts[i].ip, sym->name,
>  			       counts[i].count);
>  		} else {
> diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
> index d08046ab81f0..bc8e6afdae6d 100644
> --- a/samples/bpf/trace_event_user.c
> +++ b/samples/bpf/trace_event_user.c
> @@ -34,6 +34,11 @@ static void print_ksym(__u64 addr)
>  	if (!addr)
>  		return;
>  	sym = ksym_search(addr);
> +	if (!sym){
> +		printf("ksym not found. Is kallsyms loaded?\n");
> +		return;
> +	}
> +
>  	printf("%s;", sym->name);
>  	if (!strcmp(sym->name, "sys_read"))
>  		sys_read_seen = true;
>