Messages in this thread | | | Date | Wed, 11 Sep 2019 16:20:48 +0100 | From | Eugene Syromiatnikov <> | Subject | Re: [PATCH v2] fork: check exit_signal passed in clone3() call |
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On Wed, Sep 11, 2019 at 04:54:47PM +0200, Christian Brauner wrote: > On Wed, Sep 11, 2019 at 03:32:13PM +0100, Eugene Syromiatnikov wrote: > > On Wed, Sep 11, 2019 at 04:16:36PM +0200, Christian Brauner wrote: > > > On Wed, Sep 11, 2019 at 03:52:36PM +0200, Christian Brauner wrote: > > > > On Wed, Sep 11, 2019 at 06:48:52AM -0700, Andrew Morton wrote: > > > > > What are the user-visible runtime effects of this bug? > > > > The userspace can set -1 as an exit_signal, and that will break process > > signalling and reaping. > > > > > > > Relatedly, should this fix be backported into -stable kernels? If so, why? > > > > > > > > No, as I said in my other mail clone3() is not in any released kernel > > > > yet. clone3() is going to be released in v5.3. > > > > > > Sigh, I spoke to soon... Hm, this is placed in _do_fork(). There's a > > > chance that this might be visible in legacy clone if anyone passes in an > > > invalid signal greater than NSIG right now somehow, they'd now get > > > EINVAL if I'm seeing this right. > > > > > > So an alternative might be to only fix this in clone3() only right now > > > and get this patch into 5.3 to not release clone3() with this bug from > > > legacy clone duplicated. > > > And we defer the actual legacy clone fix until after next merge window > > > having it stew in linux-next for a couple of rcs. Distros often pull in > > > rcs so if anyone notices a regression for legacy clone we'll know about > > > it... valid_signal() checks at process exit time when the parent is > > > supposed to be notifed will catch faulty signals anyway so it's not that > > > big of a deal. > > > > As the patch is written, only copy_clone_args_from_user is touched (which > > is used only by clone3 and not legacy clone), and the check added > > Great! > > > replicates legacy clone behaviour: userspace can set 0..CSIGNAL > > as an exit_signal. Having ability to set exit_signal in NSIG..CSIGNAL > > Hm. The way I see it for clone3() it would make sense to only have < > NSIG right away. valid_signal() won't let through anything else > anyway... Since clone3() isn't out yet it doesn't make sense to > replicate the (buggy) behavior of legacy clone, right?
I was thinking about that and in the end decided to go with CSIGNAL; the only issue I see here is that it prevents for libc to easily switch clone() library call implementation to clone3(), in case there are some applications that rely on this kind of behaviour; if there's no such userspace users, then switch to valid_signal() check for both legacy and clone3 should be fine (along with possible switching to u64 for kernel_clone_args's exit_signal, so the check can done in one place), but I'm agree with your hesitance to do it right now.
> Christian
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