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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH 4.4 126/131] KVM: Reject device ioctls from processes other than the VMs creator
Date:   Mon,  1 Apr 2019 19:03:16 +0200
Message-Id: <20190401170101.968728808@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sean Christopherson <sean.j.christopherson@intel.com>

commit ddba91801aeb5c160b660caed1800eb3aef403f8 upstream.

KVM's API requires thats ioctls must be issued from the same process
that created the VM.  In other words, userspace can play games with a
VM's file descriptors, e.g. fork(), SCM_RIGHTS, etc..., but only the
creator can do anything useful.  Explicitly reject device ioctls that
are issued by a process other than the VM's creator, and update KVM's
API documentation to extend its requirements to device ioctls.

Fixes: 852b6d57dc7f ("kvm: add device control API")
Cc: <stable@vger.kernel.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 Documentation/virtual/kvm/api.txt |   16 +++++++++++-----
 virt/kvm/kvm_main.c               |    3 +++
 2 files changed, 14 insertions(+), 5 deletions(-)

--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -13,7 +13,7 @@ of a virtual machine.  The ioctls belong
 
  - VM ioctls: These query and set attributes that affect an entire virtual
    machine, for example memory layout.  In addition a VM ioctl is used to
-   create virtual cpus (vcpus).
+   create virtual cpus (vcpus) and devices.
 
    Only run VM ioctls from the same process (address space) that was used
    to create the VM.
@@ -24,6 +24,11 @@ of a virtual machine.  The ioctls belong
    Only run vcpu ioctls from the same thread that was used to create the
    vcpu.
 
+ - device ioctls: These query and set attributes that control the operation
+   of a single device.
+
+   device ioctls must be issued from the same process (address space) that
+   was used to create the VM.
 
 2. File descriptors
 -------------------
@@ -32,10 +37,11 @@ The kvm API is centered around file desc
 open("/dev/kvm") obtains a handle to the kvm subsystem; this handle
 can be used to issue system ioctls.  A KVM_CREATE_VM ioctl on this
 handle will create a VM file descriptor which can be used to issue VM
-ioctls.  A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu
-and return a file descriptor pointing to it.  Finally, ioctls on a vcpu
-fd can be used to control the vcpu, including the important task of
-actually running guest code.
+ioctls.  A KVM_CREATE_VCPU or KVM_CREATE_DEVICE ioctl on a VM fd will
+create a virtual cpu or device and return a file descriptor pointing to
+the new resource.  Finally, ioctls on a vcpu or device fd can be used
+to control the vcpu or device.  For vcpus, this includes the important
+task of actually running guest code.
 
 In general file descriptors can be migrated among processes by means
 of fork() and the SCM_RIGHTS facility of unix domain socket.  These
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2611,6 +2611,9 @@ static long kvm_device_ioctl(struct file
 {
 	struct kvm_device *dev = filp->private_data;
 
+	if (dev->kvm->mm != current->mm)
+		return -EIO;
+
 	switch (ioctl) {
 	case KVM_SET_DEVICE_ATTR:
 		return kvm_device_ioctl_attr(dev, dev->ops->set_attr, arg);