On 4/10/19 12:58 AM, Daniel Borkmann wrote:
> On 04/10/2019 02:37 AM, Yonghong Song wrote:
>> The issue is reported at https://github.com/libbpf/libbpf/issues/28.
>>
>> Basically, per C standard, for
>>    void *memcpy(void *dest, const void *src, size_t n)
>> if "dest" or "src" is NULL, regardless of whether "n" is 0 or not,
>> the result of memcpy is undefined. clang ubsan reported three such
>> instances in bpf.c with the following pattern:
>>    memcpy(dest, 0, 0).
>>
>> Although in practice, no known compiler will cause issues when
>> copy size is 0. Let us still fix the issue to silence ubsan
>> warnings.
>>
>> Signed-off-by: Yonghong Song <y...@fb.com>
> 
> Applied, thanks. I fixed up $SUBJECT while applying to add a subsystem prefix.
> 
>> ---
>>   tools/lib/bpf/bpf.c | 19 +++++++++----------
>>   1 file changed, 9 insertions(+), 10 deletions(-)
>>
>> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
>> index a1db869a6fda..78f2400dd2d1 100644
>> --- a/tools/lib/bpf/bpf.c
>> +++ b/tools/lib/bpf/bpf.c
>> @@ -79,7 +79,6 @@ static inline int sys_bpf_prog_load(union bpf_attr *attr, 
>> unsigned int size)
>>   
>>   int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
>>   {
>> -    __u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
>>      union bpf_attr attr;
>>   
>>      memset(&attr, '\0', sizeof(attr));
>> @@ -89,8 +88,9 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr 
>> *create_attr)
>>      attr.value_size = create_attr->value_size;
>>      attr.max_entries = create_attr->max_entries;
>>      attr.map_flags = create_attr->map_flags;
>> -    memcpy(attr.map_name, create_attr->name,
>> -           min(name_len, BPF_OBJ_NAME_LEN - 1));
>> +    if (create_attr->name)
>> +            memcpy(attr.map_name, create_attr->name,
>> +                   min(strlen(create_attr->name), BPF_OBJ_NAME_LEN - 1));
> 
> Any reason we don't simplify this to use strncpy() for all these occurrences?
No particular reason, just did not think that far :-)
Yes, strncpy instead of memcpy should work here as well.

> 
> Thanks,
> Daniel
> 

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