Re: [PATCH net] vhost: fix OOB in get_rx_bufs()

[Stefan Hajnoczi]

On Mon, Jan 28, 2019 at 03:05:05PM +0800, Jason Wang wrote:
> After batched used ring updating was introduced in commit e2b3b35eb989
> ("vhost_net: batch used ring update in rx"). We tend to batch heads in
> vq->heads for more than one packet. But the quota passed to
> get_rx_bufs() was not correctly limited, which can result a OOB write
> in vq->heads.
> 
>         headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
>                     vhost_len, &in, vq_log, &log,
>                     likely(mergeable) ? UIO_MAXIOV : 1);
> 
> UIO_MAXIOV was still used which is wrong since we could have batched
> used in vq->heads, this will cause OOB if the next buffer needs more
> than 960 (1024 (UIO_MAXIOV) - 64 (VHOST_NET_BATCH)) heads after we've
> batched 64 (VHOST_NET_BATCH) heads:
> 
> =============================================================================
> BUG kmalloc-8k (Tainted: G    B            ): Redzone overwritten
> -----------------------------------------------------------------------------
> 
> INFO: 0x00000000fd93b7a2-0x00000000f0713384. First byte 0xa9 instead of 0xcc
> INFO: Allocated in alloc_pd+0x22/0x60 age=3933677 cpu=2 pid=2674
>     kmem_cache_alloc_trace+0xbb/0x140
>     alloc_pd+0x22/0x60
>     gen8_ppgtt_create+0x11d/0x5f0
>     i915_ppgtt_create+0x16/0x80
>     i915_gem_create_context+0x248/0x390
>     i915_gem_context_create_ioctl+0x4b/0xe0
>     drm_ioctl_kernel+0xa5/0xf0
>     drm_ioctl+0x2ed/0x3a0
>     do_vfs_ioctl+0x9f/0x620
>     ksys_ioctl+0x6b/0x80
>     __x64_sys_ioctl+0x11/0x20
>     do_syscall_64+0x43/0xf0
>     entry_SYSCALL_64_after_hwframe+0x44/0xa9
> INFO: Slab 0x00000000d13e87af objects=3 used=3 fp=0x          (null) flags=0x200000000010201
> INFO: Object 0x0000000003278802 @offset=17064 fp=0x00000000e2e6652b
> 
> Fixing this by allocating UIO_MAXIOV + VHOST_NET_BATCH iovs for
> vhost-net. This is done through set the limitation through
> vhost_dev_init(), then set_owner can allocate the number of iov in a
> per device manner.
> 
> This fixes CVE-2018-16880.
> 
> Fixes: e2b3b35eb989 ("vhost_net: batch used ring update in rx")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
>  drivers/vhost/net.c   | 3 ++-
>  drivers/vhost/scsi.c  | 2 +-
>  drivers/vhost/vhost.c | 7 ++++---
>  drivers/vhost/vhost.h | 4 +++-
>  drivers/vhost/vsock.c | 2 +-
>  5 files changed, 11 insertions(+), 7 deletions(-)

No change in the scsi and vsock cases.  I haven't reviewed the net case.

Acked-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>

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