Re: [PATCH v3 3/7] kprobes: validate the symbol name length

[Naveen N. Rao]

Excerpts from Michael Ellerman's message of April 20, 2017 11:38:
> "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> writes:
>
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 6a128f3a7ed1..bb86681c8a10 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1382,6 +1382,28 @@ bool within_kprobe_blacklist(unsigned long addr)
> >  	return false;
> >  }
> >  
> > +bool is_valid_kprobe_symbol_name(const char *name)
> > +{
> > +	size_t sym_len;
> > +	char *s;
> > +
> > +	s = strchr(name, ':');
> > +	if (s) {
> > +		sym_len = strnlen(s+1, KSYM_NAME_LEN);
> > +		if (sym_len <= 0 || sym_len >= KSYM_NAME_LEN)
> > +			return false;
> > +		sym_len = (size_t)(s - name);
> > +		if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
> > +			return false;
> > +	} else {
> > +		sym_len = strnlen(name, MODULE_NAME_LEN);
> > +		if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
> > +			return false;
> > +	}
>
> I think this is probably more elaborate than it needs to be.
>
> Why not just check the string is <= (MODULE_NAME_LEN + KSYM_NAME_LEN) ?

Yes, that would be sufficient for now.

It's probably just me being paranoid, but I felt it's good to have 
stricter checks for user-provided strings, to guard against future 
changes to how we process this.

- Naveen