Re: [PATCH] aio: Fix io_pgetevents() struct __compat_aio_sigset layout

[Christoph Hellwig <hch@lst.de>]

On Wed, Aug 21, 2019 at 05:38:20AM +0200, Guillem Jover wrote:
> This type is used to pass the sigset_t from userland to the kernel,
> but it was using the kernel native pointer type for the member
> representing the compat userland pointer to the userland sigset_t.
> 
> This messes up the layout, and makes the kernel eat up both the
> userland pointer and the size members into the kernel pointer, and
> then reads garbage into the kernel sigsetsize. Which makes the sigset_t
> size consistency check fail, and consequently the syscall always
> returns -EINVAL.
> 
> This breaks both libaio and strace on 32-bit userland running on 64-bit
> kernels. And there are apparently no users in the wild of the current
> broken layout (at least according to codesearch.debian.org and a brief
> check over github.com search). So it looks safe to fix this directly
> in the kernel, instead of either letting userland deal with this
> permanently with the additional overhead or trying to make the syscall
> infer what layout userland used, even though this is also being worked
> around in libaio to temporarily cope with kernels that have not yet
> been fixed.
> 
> We use a proper compat_uptr_t instead of a compat_sigset_t pointer.
> 
> Fixes: 7a074e96 ("aio: implement io_pgetevents")
> Signed-off-by: Guillem Jover <guillem@hadrons.org>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>