Re: [PATCH] KVM: fix an error code in kvm_create_vm()

[Sean Christopherson]

On Thu, Jun 13, 2024, Dan Carpenter wrote:
> This error path used to return -ENOMEM from the where r is initialized
> at the top of the function.  But a new "r = kvm_init_irq_routing(kvm);"
> was introduced in the middle of the function so now the error code is
> not set and it eventually leads to a NULL dereference.  Set the error
> code back to -ENOMEM.
> 
> Fixes: fbe4a7e881d4 ("KVM: Setup empty IRQ routing when creating a VM")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
>  virt/kvm/kvm_main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 07ec9b67a202..ea7e32d722c9 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1212,8 +1212,10 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  	for (i = 0; i < KVM_NR_BUSES; i++) {
>  		rcu_assign_pointer(kvm->buses[i],
>  			kzalloc(sizeof(struct kvm_io_bus), GFP_KERNEL_ACCOUNT));
> -		if (!kvm->buses[i])
> +		if (!kvm->buses[i]) {
> +			r = -ENOMEM;
>  			goto out_err_no_arch_destroy_vm;
> +		}
>  	}

Drat.  Any objection to tweaking this slightly to guard against similar bugs in
the future?  If not, I'll apply+push the below.

Thanks!

--
From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Date: Thu, 13 Jun 2024 17:33:16 +0300
Subject: [PATCH] KVM: fix an error code in kvm_create_vm()

This error path used to return -ENOMEM from the where r is initialized
at the top of the function.  But a new "r = kvm_init_irq_routing(kvm);"
was introduced in the middle of the function so now the error code is
not set and it eventually leads to a NULL dereference.  Set the error
code back to -ENOMEM.

Opportunistically tweak the logic to pre-set "r = -ENOMEM" immediately
before the flows that can fail due to memory allocation failure to make
it less likely that the bug recurs in the future.

Fixes: fbe4a7e881d4 ("KVM: Setup empty IRQ routing when creating a VM")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Link: https://lore.kernel.org/r/02051e0a-09d8-49a2-917f-7c2f278a1ba1@moroto.mountain
[sean: tweak all of the "r = -ENOMEM" sites]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 virt/kvm/kvm_main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b60186b9c1d3..436ca41f61e5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1143,8 +1143,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 {
 	struct kvm *kvm = kvm_arch_alloc_vm();
 	struct kvm_memslots *slots;
-	int r = -ENOMEM;
-	int i, j;
+	int r, i, j;
 
 	if (!kvm)
 		return ERR_PTR(-ENOMEM);
@@ -1181,6 +1180,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 	snprintf(kvm->stats_id, sizeof(kvm->stats_id), "kvm-%d",
 		 task_pid_nr(current));
 
+	r = -ENOMEM;
 	if (init_srcu_struct(&kvm->srcu))
 		goto out_err_no_srcu;
 	if (init_srcu_struct(&kvm->irq_srcu))
@@ -1209,6 +1209,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 		rcu_assign_pointer(kvm->memslots[i], &kvm->__memslots[i][0]);
 	}
 
+	r = -ENOMEM;
 	for (i = 0; i < KVM_NR_BUSES; i++) {
 		rcu_assign_pointer(kvm->buses[i],
 			kzalloc(sizeof(struct kvm_io_bus), GFP_KERNEL_ACCOUNT));

base-commit: 3dee3b187499b317a6587e2b8e9bf3d5050e5288
--