lkml.org 
[lkml]   [2022]   [Jul]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 5.15 126/230] KVM: Initialize debugfs_dentry when a VM is created to avoid NULL deref
    Date
    From: Sean Christopherson <seanjc@google.com>

    [ Upstream commit 5c697c367a66307a5d943c3449421aff2aa3ca4a ]

    Initialize debugfs_entry to its semi-magical -ENOENT value when the VM
    is created. KVM's teardown when VM creation fails is kludgy and calls
    kvm_uevent_notify_change() and kvm_destroy_vm_debugfs() even if KVM never
    attempted kvm_create_vm_debugfs(). Because debugfs_entry is zero
    initialized, the IS_ERR() checks pass and KVM derefs a NULL pointer.

    BUG: kernel NULL pointer dereference, address: 0000000000000018
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    PGD 1068b1067 P4D 1068b1067 PUD 1068b0067 PMD 0
    Oops: 0000 [#1] SMP
    CPU: 0 PID: 871 Comm: repro Not tainted 5.18.0-rc1+ #825
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
    RIP: 0010:__dentry_path+0x7b/0x130
    Call Trace:
    <TASK>
    dentry_path_raw+0x42/0x70
    kvm_uevent_notify_change.part.0+0x10c/0x200 [kvm]
    kvm_put_kvm+0x63/0x2b0 [kvm]
    kvm_dev_ioctl+0x43a/0x920 [kvm]
    __x64_sys_ioctl+0x83/0xb0
    do_syscall_64+0x31/0x50
    entry_SYSCALL_64_after_hwframe+0x44/0xae
    </TASK>
    Modules linked in: kvm_intel kvm irqbypass

    Fixes: a44a4cc1c969 ("KVM: Don't create VM debugfs files outside of the VM directory")
    Cc: stable@vger.kernel.org
    Cc: Marc Zyngier <maz@kernel.org>
    Cc: Oliver Upton <oupton@google.com>
    Reported-by: syzbot+df6fbbd2ee39f21289ef@syzkaller.appspotmail.com
    Signed-off-by: Sean Christopherson <seanjc@google.com>
    Reviewed-by: Oliver Upton <oupton@google.com>
    Message-Id: <20220415004622.2207751-1-seanjc@google.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    virt/kvm/kvm_main.c | 12 ++++++------
    1 file changed, 6 insertions(+), 6 deletions(-)

    diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    index 9134ae252d7c..9eac68ae291e 100644
    --- a/virt/kvm/kvm_main.c
    +++ b/virt/kvm/kvm_main.c
    @@ -934,12 +934,6 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
    int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
    kvm_vcpu_stats_header.num_desc;

    - /*
    - * Force subsequent debugfs file creations to fail if the VM directory
    - * is not created.
    - */
    - kvm->debugfs_dentry = ERR_PTR(-ENOENT);
    -
    if (!debugfs_initialized())
    return 0;

    @@ -1055,6 +1049,12 @@ static struct kvm *kvm_create_vm(unsigned long type)

    BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX);

    + /*
    + * Force subsequent debugfs file creations to fail if the VM directory
    + * is not created (by kvm_create_vm_debugfs()).
    + */
    + kvm->debugfs_dentry = ERR_PTR(-ENOENT);
    +
    if (init_srcu_struct(&kvm->srcu))
    goto out_err_no_srcu;
    if (init_srcu_struct(&kvm->irq_srcu))
    --
    2.35.1


    \
     
     \ /
      Last update: 2022-07-11 11:52    [W:3.833 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site