Re: [PATCH] KVM: PPC: Book3S: Fix race and leak in kvm_vm_ioctl_create_spapr_tce()

David Gibson
2017-08-24T03:56:32Z

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On Thu, Aug 24, 2017 at 01:40:08PM +1000, Paul Mackerras wrote:
> Nixiaoming pointed out that there is a memory leak in
> kvm_vm_ioctl_create_spapr_tce() if the call to anon_inode_getfd()
> fails; the memory allocated for the kvmppc_spapr_tce_table struct
> is not freed, and nor are the pages allocated for the iommu
> tables. In addition, we have already incremented the process's
> count of locked memory pages, and this doesn't get restored on
> error.
>
> David Hildenbrand pointed out that there is a race in that the
> function checks early on that there is not already an entry in the
> stt->iommu_tables list with the same LIOBN, but an entry with the
> same LIOBN could get added between then and when the new entry is
> added to the list.
>
> This fixes all three problems. To simplify things, we now call
> anon_inode_getfd() before placing the new entry in the list. The
> check for an existing entry is done while holding the kvm->lock
> mutex, immediately before adding the new entry to the list.
> Finally, on failure we now call kvmppc_account_memlimit to
> decrement the process's count of locked memory pages.
>
> Reported-by: Nixiaoming <nixiaoming@huawei.com>
> Reported-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> arch/powerpc/kvm/book3s_64_vio.c | 55 ++++++++++++++++++++++++----------------
> 1 file changed, 33 insertions(+), 22 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index a160c14304eb..d463c1cd0d8d 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -297,29 +297,22 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> unsigned long npages, size;
> int ret = -ENOMEM;
> int i;
> + int fd = -1;
>
> if (!args->size)
> return -EINVAL;
>
> - /* Check this LIOBN hasn't been previously allocated */
> - list_for_each_entry(stt, &kvm->arch.spapr_tce_tables, list) {
> - if (stt->liobn == args->liobn)
> - return -EBUSY;
> - }
> -
> size = _ALIGN_UP(args->size, PAGE_SIZE >> 3);
> npages = kvmppc_tce_pages(size);
> ret = kvmppc_account_memlimit(kvmppc_stt_pages(npages), true);
> - if (ret) {
> - stt = NULL;
> - goto fail;
> - }
> + if (ret)
> + return ret;
>
> ret = -ENOMEM;
> stt = kzalloc(sizeof(*stt) + npages * sizeof(struct page *),
> GFP_KERNEL);
> if (!stt)
> - goto fail;
> + goto fail_acct;
>
> stt->liobn = args->liobn;
> stt->page_shift = args->page_shift;
> @@ -334,24 +327,42 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> goto fail;
> }
>
> - kvm_get_kvm(kvm);
> + ret = fd = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,
> + stt, O_RDWR | O_CLOEXEC);
> + if (ret < 0)
> + goto fail;
>
> mutex_lock(&kvm->lock);
> - list_add_rcu(&stt->list, &kvm->arch.spapr_tce_tables);
> +
> + /* Check this LIOBN hasn't been previously allocated */
> + ret = 0;
> + list_for_each_entry(stt, &kvm->arch.spapr_tce_tables, list) {
> + if (stt->liobn == args->liobn) {
> + ret = -EBUSY;
> + break;
> + }
> + }
> +
> + if (!ret) {
> + list_add_rcu(&stt->list, &kvm->arch.spapr_tce_tables);
> + kvm_get_kvm(kvm);
> + }
>
> mutex_unlock(&kvm->lock);
>
> - return anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,
> - stt, O_RDWR | O_CLOEXEC);
> + if (!ret)
> + return fd;
>
> -fail:
> - if (stt) {
> - for (i = 0; i < npages; i++)
> - if (stt->pages[i])
> - __free_page(stt->pages[i]);
> + put_unused_fd(fd);
>
> - kfree(stt);
> - }
> + fail:
> + for (i = 0; i < npages; i++)
> + if (stt->pages[i])
> + __free_page(stt->pages[i]);
> +
> + kfree(stt);
> + fail_acct:
> + kvmppc_account_memlimit(kvmppc_stt_pages(npages), false);
> return ret;
> }
>

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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