linux-kernel - [PATCH 4.14 21/43] scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue

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Message-Id: <20190702080124.907127322@linuxfoundation.org>
Date:   Tue,  2 Jul 2019 10:02:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Ewan D. Milne" <emilne@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: [PATCH 4.14 21/43] scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue_lck()

From: Jan Kara <jack@...e.cz>

commit 240b4cc8fd5db138b675297d4226ec46594d9b3b upstream.

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@...r.kernel.org>
Signed-off-by: Jan Kara <jack@...e.cz>
Reviewed-by: Ewan D. Milne <emilne@...hat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/scsi/vmw_pvscsi.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/scsi/vmw_pvscsi.c
+++ b/drivers/scsi/vmw_pvscsi.c
@@ -763,6 +763,7 @@ static int pvscsi_queue_lck(struct scsi_
 	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_
 	}

 	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;
 }