On Thu, Feb 23, 2012 at 11:38 AM, Roland McGrath <mcgrathr@xxxxxxxxxx> wrote: > On Wed, Feb 22, 2012 at 5:06 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> I meant whether or not a signal can be blocked/caught and the fact that >> the signal exists at all. >> >> Now I guess we could have "blockable" and "unblockable" SIGSYS, but that >> would seem to have its own set of issues... > > Oh. I certainly don't think we should ever add any new signals to the set > that cannot be caught, blocked, or ignored. That has been just SIGKILL and > SIGSTOP since 4.2BSD, which first introduced the modern concept of blocking > signals. There are lots of reasons not to change that, which I won't go > into unless someone really wants me to. > > However, I don't think there is anything really wrong with having certain > cases that generate a signal and at the same time unblock it and reset it > to SIG_DFL. That's just an implementation detail of a policy of "dump core > right now, no other option". (Conversely, directly calling do_exit won't > ever dump core, though it can be made to look signalesque to the parent and > tracers.) > > For seccomp-filter, I personally don't see any problem with simply > generating SIGSYS in the normal way (and aborting the syscall, of course). > If someone wants to ensure that SIGSYS is never caught or blocked, they can > just do that by having a filter that doesn't allow it to be caught or > blocked (and of course make sure to reset its inherited state). It is a > bit tricky to cover all the ways, since it's not just sigaction and > sigprocmask but also sigreturn, where the blocked signal set to be restored > is in a slightly arcane location--but it ain't rocket science. > > But I don't really have any strong opinion about what seccomp-filter should > do. (Though it does seem worthwhile not to rule out the possibility of > dumping core on a policy violation, since that will be useful for people to > debug their code.) Seems like there's an argument for another return code, SECCOMP_RET_CORE, that resets/unblocks the SIGSYS handler since the existing TRAP and KILL options seem to cover the other paths (signal handler and do_exit). It's a very small tweak if that'd be useful to include explicitly. Thanks! will -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
