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SubjectRe: [PATCH] vhost: zero vhost_vsock memory on allocation
On Tue, Mar 26, 2019 at 08:56:14PM -0400, Vitaly Mayatskikh wrote:
> This fixes OOPS when using under-initialized vhost_vsock object.
>
> The code had a combo of kzalloc plus vmalloc as a fallback
> initially, but it has been replaced by plain kvmalloc in
> commit 6c5ab6511f71 ("mm: support __GFP_REPEAT in kvmalloc_node for >32kB")
>
> OOPS is easy to reproduce with open/ioctl after trashing the RAM.

Which field was accessed before initialization?

I ask because the situation is now unclear since code remains that
assumes vsock is *not* zero-initialized:

vsock->guest_cid = 0; /* no CID assigned yet */

atomic_set(&vsock->queued_replies, 0);

If we're going to zalloc, let's get rid of explicit zero
initializations. Or let's use kvmalloc() and fix the uninitialized
access. Mixing both is confusing.

> Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
> ---
> drivers/vhost/vsock.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index bb5fc0e..9e7cb13 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -512,7 +512,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
> /* This struct is large and allocation could fail, fall back to vmalloc
> * if there is no other way.
> */
> - vsock = kvmalloc(sizeof(*vsock), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> + vsock = kvzalloc(sizeof(*vsock), GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> if (!vsock)
> return -ENOMEM;
>
> --
> 1.8.3.1
>
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