Commit 71aa687b authored by Salvatore Bonaccorso's avatar Salvatore Bonaccorso

kvm: fix kvm_ioctl_create_device() reference counting (CVE-2019-6974)

parent e898a5d9
......@@ -392,6 +392,7 @@ linux (4.19.20-1) UNRELEASED; urgency=medium
[ Salvatore Bonaccorso ]
* [x86] kvmclock: set offset for kvm unstable clock (Closes: #918036)
* kvm: fix kvm_ioctl_create_device() reference counting (CVE-2019-6974)
[ Hideki Yamane ]
* [x86] Enable Touchpad support on Gemini Lake via CONFIG_PINCTRL_GEMINILAKE
From: Jann Horn <>
Date: Sat, 26 Jan 2019 01:54:33 +0100
Subject: kvm: fix kvm_ioctl_create_device() reference counting (CVE-2019-6974)
kvm_ioctl_create_device() does the following:
1. creates a device that holds a reference to the VM object (with a borrowed
reference, the VM's refcount has not been bumped yet)
2. initializes the device
3. transfers the reference to the device to the caller's file descriptor table
4. calls kvm_get_kvm() to turn the borrowed reference to the VM into a real
The ownership transfer in step 3 must not happen before the reference to the VM
becomes a proper, non-borrowed reference, which only happens in step 4.
After step 3, an attacker can close the file descriptor and drop the borrowed
reference, which can cause the refcount of the kvm object to drop to zero.
This means that we need to grab a reference for the device before
anon_inode_getfd(), otherwise the VM can disappear from under us.
Fixes: 852b6d57dc7f ("kvm: add device control API")
Signed-off-by: Jann Horn <>
Signed-off-by: Paolo Bonzini <>
virt/kvm/kvm_main.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5ecea812cb6a..585845203db8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3000,8 +3000,10 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
if (ops->init)
+ kvm_get_kvm(kvm);
ret = anon_inode_getfd(ops->name, &kvm_device_fops, dev, O_RDWR | O_CLOEXEC);
if (ret < 0) {
+ kvm_put_kvm(kvm);
@@ -3009,7 +3011,6 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
return ret;
- kvm_get_kvm(kvm);
cd->fd = ret;
return 0;
......@@ -139,6 +139,7 @@ features/all/lockdown/arm64-add-kernel-config-option-to-lock-down-when.patch
# Security fixes
# Fix exported symbol versions
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