Hi,
On 11/7/2021 3:26 AM, Alexei Starovoitov wrote:
> On Sat, Nov 06, 2021 at 09:28:21PM +0800, Hou Tao wrote:
>> The helper compares two strings: one string is a null-terminated
>> read-only string, and another one has const max storage size. And
>> it can be used to compare file name in tracing or LSM program.
>>
>> We don't check whether or not s2 in bpf_strncmp() is null-terminated,
>> because its content may be changed by malicous program, and we only
>> ensure the memory accessed is bounded by s2_sz.
> I think "malicous" adjective is unnecessary and misleading.
> It's also misspelled.
> Just mention that 2nd argument doesn't have to be null terminated.
Will do.
>> + * long bpf_strncmp(const char *s1, const char *s2, u32 s2_sz)
> ...
>> +BPF_CALL_3(bpf_strncmp, const char *, s1, const char *, s2, size_t, s2_sz)
> probably should match u32 instead of size_t.
Yes, will use u32 instead. I forgot to synchronize between these two declarations.
>
>> @@ -1210,6 +1210,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>> return &bpf_get_branch_snapshot_proto;
>> case BPF_FUNC_trace_vprintk:
>> return bpf_get_trace_vprintk_proto();
>> + case BPF_FUNC_strncmp:
>> + return &bpf_strncmp_proto;
> why tracing only?
> Should probably be in bpf_base_func_proto.
Because in our use case, bpf_strncmp() is only used by tracing program, but moving
it to bpf_base_func_proto() incurs no harm, so will do it.
>
> I was thinking whether the proto could be:
> long bpf_strncmp(const char *s1, u32 s1_sz, const char *s2)
> but I think your version is better though having const string as 1st arg
> is a bit odd in normal C.
>
> Would it make sense to add bpf_memchr as well while we are at it?
> And
> static inline bpf_strnlen(const char *s, u32 sz)
> {
> return bpf_memchr(s, sz, 0);
> }
> to bpf_helpers.h ?
> .
It is OK to add it, although I don't have a use case for it.
