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.
> + * 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.
> @@ -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.
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 ?
