[PATCH] scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue_lck()

[PATCH] scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue_lck()

[Jan Kara]

Once we unlock adapter->hw_lock in pvscsi_queue_lck() nothing prevents just
queued scsi_cmnd from completing and freeing the request. Thus cmd->cmnd[0]
dereference can dereference already freed request leading to kernel crashes or
other issues (which one of our customers observed). Store cmd->cmnd[0] in a
local variable before unlocking adapter->hw_lock to fix the issue.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 drivers/scsi/vmw_pvscsi.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/vmw_pvscsi.c b/drivers/scsi/vmw_pvscsi.c
index ecee4b3ff073..377b07b2feeb 100644
--- a/drivers/scsi/vmw_pvscsi.c
+++ b/drivers/scsi/vmw_pvscsi.c
@@ -763,6 +763,7 @@ static int pvscsi_queue_lck(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd
 	struct pvscsi_adapter *adapter = shost_priv(host);
 	struct pvscsi_ctx *ctx;
 	unsigned long flags;
+	unsigned char op;
 
 	spin_lock_irqsave(&adapter->hw_lock, flags);
 
@@ -775,13 +776,14 @@ static int pvscsi_queue_lck(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd
 	}
 
 	cmd->scsi_done = done;
+	op = cmd->cmnd[0];
 
 	dev_dbg(&cmd->device->sdev_gendev,
-		"queued cmd %p, ctx %p, op=%x\n", cmd, ctx, cmd->cmnd[0]);
+		"queued cmd %p, ctx %p, op=%x\n", cmd, ctx, op);
 
 	spin_unlock_irqrestore(&adapter->hw_lock, flags);
 
-	pvscsi_kick_io(adapter, cmd->cmnd[0]);
+	pvscsi_kick_io(adapter, op);
 
 	return 0;
 }
-- 
2.16.4

Re: [PATCH] scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue_lck()

[Ewan D. Milne]

On Wed, 2019-06-19 at 09:05 +0200, Jan Kara wrote:
> Once we unlock adapter->hw_lock in pvscsi_queue_lck() nothing prevents just
> queued scsi_cmnd from completing and freeing the request. Thus cmd->cmnd[0]
> dereference can dereference already freed request leading to kernel crashes or
> other issues (which one of our customers observed). Store cmd->cmnd[0] in a
> local variable before unlocking adapter->hw_lock to fix the issue.
> 
> CC: stable@vger.kernel.org
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  drivers/scsi/vmw_pvscsi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/vmw_pvscsi.c b/drivers/scsi/vmw_pvscsi.c
> index ecee4b3ff073..377b07b2feeb 100644
> --- a/drivers/scsi/vmw_pvscsi.c
> +++ b/drivers/scsi/vmw_pvscsi.c
> @@ -763,6 +763,7 @@ static int pvscsi_queue_lck(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd
>  	struct pvscsi_adapter *adapter = shost_priv(host);
>  	struct pvscsi_ctx *ctx;
>  	unsigned long flags;
> +	unsigned char op;
>  
>  	spin_lock_irqsave(&adapter->hw_lock, flags);
>  
> @@ -775,13 +776,14 @@ static int pvscsi_queue_lck(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd
>  	}
>  
>  	cmd->scsi_done = done;
> +	op = cmd->cmnd[0];
>  
>  	dev_dbg(&cmd->device->sdev_gendev,
> -		"queued cmd %p, ctx %p, op=%x\n", cmd, ctx, cmd->cmnd[0]);
> +		"queued cmd %p, ctx %p, op=%x\n", cmd, ctx, op);
>  
>  	spin_unlock_irqrestore(&adapter->hw_lock, flags);
>  
> -	pvscsi_kick_io(adapter, cmd->cmnd[0]);
> +	pvscsi_kick_io(adapter, op);
>  
>  	return 0;
>  }

Reviewed-by: Ewan D. Milne <emilne@redhat.com>

Re: [PATCH] scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue_lck()

[Martin K. Petersen]

Jan,

> Once we unlock adapter->hw_lock in pvscsi_queue_lck() nothing prevents
> just queued scsi_cmnd from completing and freeing the request. Thus
> cmd->cmnd[0] dereference can dereference already freed request leading
> to kernel crashes or other issues (which one of our customers
> observed). Store cmd->cmnd[0] in a local variable before unlocking
> adapter->hw_lock to fix the issue.

Applied to 5.2/scsi-fixes. Thanks!

-- 
Martin K. Petersen	Oracle Linux Engineering