Messages in this thread | | | Date | Wed, 1 Nov 2017 12:05:55 +0000 | From | Mark Rutland <> | Subject | Re: [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks |
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On Tue, Oct 31, 2017 at 04:56:39PM -0700, Laura Abbott wrote: > On 10/26/2017 02:09 AM, Mark Rutland wrote: > > In Prague, Kees mentioned that it would be nice to have a mechanism to > > catch bad __{get,put}_user uses, such as the recent CVE-2017-5123 [1,2] > > issue with unsafe_put_user() in waitid(). > > > > These patches allow an optional access_ok() check to be dropped in > > arm64's __{get,put}_user() primitives. These will then BUG() if a bad > > user pointer is passed (which should only happen in the absence of an > > earlier access_ok() check).
> Turning on the option fails as soon as we hit userspace. On my buildroot > based environment I get the help text for ld.so (????) and then a message > about attempting to kill init.
Ouch. Thanks for the report, and sorry about this.
The problem is that I evaluate the ptr argument twice in __{get,put}_user(), and this may have side effects.
e.g. when the ELF loader does things like:
__put_user((elf_addr_t)p, sp++)
... we increment sp twice, and write to the wrong user address, leaving sp corrupt.
I have an additional patch [1] to fix this, which is in my arm64/access-ok branch [2].
Thanks, Mark.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=arm64/access-ok&id=ebb7ff83eb53b8810395d5cf48712a4ae6d678543 [2] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/access-ok
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