2020-09-07 18:57:52

by Rustam Kovhaev

Subject: [RESEND PATCH v2] KVM: fix memory leak in kvm_io_bus_unregister_dev()

when kmalloc() fails in kvm_io_bus_unregister_dev(), before removing
the bus, we should iterate over all other devices linked to it and call
kvm_iodevice_destructor() for them

Fixes: 90db10434b16 ("KVM: kvm_io_bus_unregister_dev() should never fail")
Cc: [email protected]
Reported-and-tested-by: [email protected]
Link: https://syzkaller.appspot.com/bug?extid=f196caa45793d6374707
Signed-off-by: Rustam Kovhaev <[email protected]>
Reviewed-by: Vitaly Kuznetsov <[email protected]>
---
v2:
- remove redundant whitespace
- remove goto statement and use if/else
- add Fixes tag
---
virt/kvm/kvm_main.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 67cd0b88a6b6..cf88233b819a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4332,7 +4332,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
struct kvm_io_device *dev)
{
- int i;
+ int i, j;
struct kvm_io_bus *new_bus, *bus;

bus = kvm_get_bus(kvm, bus_idx);
@@ -4349,17 +4349,20 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,

new_bus = kmalloc(struct_size(bus, range, bus->dev_count - 1),
GFP_KERNEL_ACCOUNT);
- if (!new_bus) {
+ if (new_bus) {
+ memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
+ new_bus->dev_count--;
+ memcpy(new_bus->range + i, bus->range + i + 1,
+ (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
+ } else {
pr_err("kvm: failed to shrink bus, removing it completely\n");
- goto broken;
+ for (j = 0; j < bus->dev_count; j++) {
+ if (j == i)
+ continue;
+ kvm_iodevice_destructor(bus->range[j].dev);
+ }
}

- memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
- new_bus->dev_count--;
- memcpy(new_bus->range + i, bus->range + i + 1,
- (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
-
-broken:
rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
synchronize_srcu_expedited(&kvm->srcu);
kfree(bus);
--
2.28.0

2020-09-11 16:06:03

by Paolo Bonzini

Subject: Re: [RESEND PATCH v2] KVM: fix memory leak in kvm_io_bus_unregister_dev()

On 07/09/20 20:55, Rustam Kovhaev wrote:
> when kmalloc() fails in kvm_io_bus_unregister_dev(), before removing
> the bus, we should iterate over all other devices linked to it and call
> kvm_iodevice_destructor() for them
>
> Fixes: 90db10434b16 ("KVM: kvm_io_bus_unregister_dev() should never fail")
> Cc: [email protected]
> Reported-and-tested-by: [email protected]
> Link: https://syzkaller.appspot.com/bug?extid=f196caa45793d6374707
> Signed-off-by: Rustam Kovhaev <[email protected]>
> Reviewed-by: Vitaly Kuznetsov <[email protected]>
> ---
> v2:
> - remove redundant whitespace
> - remove goto statement and use if/else
> - add Fixes tag
> ---
> virt/kvm/kvm_main.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67cd0b88a6b6..cf88233b819a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4332,7 +4332,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> struct kvm_io_device *dev)
> {
> - int i;
> + int i, j;
> struct kvm_io_bus *new_bus, *bus;
>
> bus = kvm_get_bus(kvm, bus_idx);
> @@ -4349,17 +4349,20 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
>
> new_bus = kmalloc(struct_size(bus, range, bus->dev_count - 1),
> GFP_KERNEL_ACCOUNT);
> - if (!new_bus) {
> + if (new_bus) {
> + memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
> + new_bus->dev_count--;
> + memcpy(new_bus->range + i, bus->range + i + 1,
> + (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
> + } else {
> pr_err("kvm: failed to shrink bus, removing it completely\n");
> - goto broken;
> + for (j = 0; j < bus->dev_count; j++) {
> + if (j == i)
> + continue;
> + kvm_iodevice_destructor(bus->range[j].dev);
> + }
> }
>
> - memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
> - new_bus->dev_count--;
> - memcpy(new_bus->range + i, bus->range + i + 1,
> - (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
> -
> -broken:
> rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
> synchronize_srcu_expedited(&kvm->srcu);
> kfree(bus);
>

Queued, thanks.

I am currently on leave so I am going through the patches and queuing
them, but I will only push kvm/next and kvm/queue next week. kvm/master
patches will be sent to Linus for the next -rc though.

Paolo