On Mon, May 18, 2015 at 12:43 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On May 15, 2015 11:31 PM, "Christoph Lameter" <cl@xxxxxxxxx> wrote: >> >> It would be best to start a complete new thread about this. You >> replied to earlier posts about ambient capabilities and >> people may not see it as a new release. >> >> > pA obeys the invariant that no bit can ever be set in pA if it is >> > not set in both pP and pI. Dropping a bit from pP or pI drops that >> > bit from pA. This ensures that existing programs that try to drop >> > capabilities still do so, with a complication. Because capability >> >> Ok that is a good improvement. >> >> > inheritance is so broken, setting KEEPCAPS, using setresuid to >> > switch to nonroot uids, or calling execve effectively drops >> > capabilities. Therefore, setresuid from root to nonroot >> > conditionally clears pA unless SECBIT_NO_SETUID_FIXUP is set. >> > Processes that don't like this can re-add bits to pA afterwards. >> > >> > The capability evolution rules are changed: >> > >> > pA' = (file caps or setuid or setgid ? 0 : pA) >> > pP' = (X & fP) | (pI & fI) | pA' >> > pI' = pI >> > pE' = (fE ? pP' : pA') >> >> Isnt this equal to >> >> pE' = (fE & pP') | pA' >> >> which does not require conditionals and is symmetric to how pP' is >> calculated. Your formula seems to indicate that pA' bits are not set if >> fE is set. However they are already set unconditionally in pP' regardless. >> This makes it more explicit I think. And I thought we are dealing with >> bitmask arithmetic here? > > I think you're right, except that fE is a Boolean, not a bit mask, so > fE | pP' is an odd thing to talk about. > > We could say (fE ? pP' : 0) | pA', which could simplify the code a tiny bit. It turns out that would be almost a pure addition of code, so I'll leave it as is. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html