netdev - Re: [PATCH iproute2 1/1] bpf: Fix segfault when custom pinning is used

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Date:   Wed, 22 Apr 2020 05:47:47 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     stephen@...workplumber.org, netdev@...r.kernel.org,
        dsahern@...il.com, aclaudi@...hat.com, daniel@...earbox.net,
        Jamal Hadi Salim <hadi@...atatu.com>
Subject: Re: [PATCH iproute2 1/1] bpf: Fix segfault when custom pinning is
 used

On 2020-04-22 2:42 a.m., Dominique Martinet wrote:
> (random review)
> 

Good review;->

> Jamal Hadi Salim wrote on Tue, Apr 21, 2020:
>> diff --git a/lib/bpf.c b/lib/bpf.c
>> index 10cf9bf4..cf636c9e 100644
>> --- a/lib/bpf.c
>> +++ b/lib/bpf.c
>> @@ -1509,12 +1509,12 @@ out:
>>   static int bpf_make_custom_path(const struct bpf_elf_ctx *ctx,
>>   				const char *todo)
>>   {
>> -	char *tmp = NULL;
>> +	char tmp[PATH_MAX] = {};
>>   	char *rem = NULL;
>>   	char *sub;
>>   	int ret;
>>   
>> -	ret = asprintf(&tmp, "%s/../", bpf_get_work_dir(ctx->type));
>> +	ret = sprintf(tmp, "%s/../", bpf_get_work_dir(ctx->type));
>>   	if (ret < 0) {
>>   		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
> 
> error check needs to be reworded,

Will reword.

  and it probably needs to use snprintf
> instead of sprintf: bpf_get_work_dir() can be up to PATH_MAX long and as
> pointed out there are strcat() afterwards so it's still possible to
> overflow this one
> 

and change to snprintf. The strcat afterwards is protected by the check
                 if (strlen(tmp) + strlen(sub) + 2 > PATH_MAX)
                         return -EINVAL;
However, since you looked at it now that i am paying closer attention
there's another bug there. The above check will return without freeing
earlier asprintf allocated "rem" variable. Sounds like separate patch.

cheers,
jamal