On Tue, Jul 27, 2021 at 02:50:19PM +0000, Al Viro wrote:
> On Tue, Jul 27, 2021 at 12:36:25PM +0200, Greg Kroah-Hartman wrote:
> > When running static analysis tools to find where signed values could
> > potentially wrap the family of d_path() functions turn out to trigger a
> > lot of mess. In evaluating the code, all of these usages seem safe, but
> > pointer math is involved so if a negative number is ever somehow passed
> > into these functions, memory can be traversed backwards in ways not
> > intended.
> >
> > Resolve all of the abuguity by just making "size" an unsigned value,
> > which takes the guesswork out of everything involved.
>
> TBH, I'm not sure it's the right approach. Huge argument passed to d_path()
> is a bad idea, no matter what. Do you really want to have the damn thing
> try and fill 3Gb of buffer, all while holding rcu_read_lock() and a global
> spinlock or two? Hell, s/3Gb/1Gb/ and it won't get any better...
>
>
> How about we do this instead:
>
> d_path(const struct path *path, char *buf, int buflen)
> {
> if (unlikely((unsigned)buflen > 0x8000)) {
> buf += (unsigned)buflen - 0x8000;
> buflen = 0x8000;
> }
> as in mainline
> }
>
> and take care of both issues?
umm ... what if someone passes in -ENOMEM as buflen? Not saying we
have such a path right now, but I could imagine it happening.
if (unlikely(buflen < 0))
return ERR_PTR(buflen);
if (unlikely(buflen > 0x8000)) {
buf += buflen - 0x8000;
buflen = 0x8000;
}
...
