Messages in this thread | | | Date | Wed, 3 Jun 2009 12:22:16 -0400 | Subject | Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE_PTR to point at unmapped space) | From | Eric Paris <> |
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On Wed, Jun 3, 2009 at 11:38 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > On Wed, 3 Jun 2009, Christoph Lameter wrote: > >> On Wed, 3 Jun 2009, Linus Torvalds wrote: >> >> > The point being that we do need to support mmap at zero. Not necessarily >> > universally, but it can't be some fixed "we don't allow that". >> >> Hmmm... Depend on some capability? CAP_SYS_PTRACE may be something >> remotely related? > > But as mentioned several times, we do have the system-wide setting in > 'mmap_min_addr' (that then can be overridden by CAP_SYS_RAWIO, so in that > sense a capability already exists). > > It defaults to 64kB in at least the x86 defconfig files, but to 0 in the > Kconfig defaults. Also, for some reason it has a "depends on SECURITY", > which means that if you just default to the old-style unix security you'll > lose it. > > So there are several ways to disable it by mistake. I don't know what > distros do.
Fedora has it on.
As I recall the only need for CONFIG_SECURITY is for the ability to override the check.
I think I could probably pretty cleanly change it to use CAP_SYS_RAWIO/SELinux permissions if CONFIG_SECURITY and just allow it for uid=0 in the non-security case? Deny it for everyone in the non-security case and make them change the /proc tunable if they need it?
-Eric
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