RE: [PATCH] IB/hfi1: Prevent a NULL dereference

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> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@xxxxxxxxxx]
> Sent: Tuesday, January 9, 2018 4:27 AM
> To: Marciniszyn, Mike <mike.marciniszyn@xxxxxxxxx>; Ruhl, Michael J
> <michael.j.ruhl@xxxxxxxxx>
> Cc: Dalessandro, Dennis <dennis.dalessandro@xxxxxxxxx>; Doug Ledford
> <dledford@xxxxxxxxxx>; Jason Gunthorpe <jgg@xxxxxxxx>; linux-
> rdma@xxxxxxxxxxxxxxx; kernel-janitors@xxxxxxxxxxxxxxx
> Subject: [PATCH] IB/hfi1: Prevent a NULL dereference
> 
> In the original code, we set "fd->uctxt" to NULL and then dereference it
> which will cause an Oops.
> 
> Fixes: f2a3bc00a03c ("IB/hfi1: Protect context array set/clear with spinlock")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> 
> diff --git a/drivers/infiniband/hw/hfi1/file_ops.c
> b/drivers/infiniband/hw/hfi1/file_ops.c
> index 82086241aac3..3de1ac94bb85 100644
> --- a/drivers/infiniband/hw/hfi1/file_ops.c
> +++ b/drivers/infiniband/hw/hfi1/file_ops.c
> @@ -763,10 +763,10 @@ static int complete_subctxt(struct hfi1_filedata *fd)
>  	}
> 
>  	if (ret) {
> +		__clear_bit(fd->subctxt, fd->uctxt->in_use_ctxts);
>  		hfi1_rcd_put(fd->uctxt);
>  		fd->uctxt = NULL;
>  		spin_lock_irqsave(&fd->dd->uctxt_lock, flags);
> -		__clear_bit(fd->subctxt, fd->uctxt->in_use_ctxts);
>  		spin_unlock_irqrestore(&fd->dd->uctxt_lock, flags);
>  	}
> 

Hi Dan,

Thanks for catching this.

However, the patch is not quite correct.

The __clear_bit() spin_lock_irqsave/restore need stay together.  The patch should be:

diff --git a/drivers/infiniband/hw/hfi1/file_ops.c b/drivers/infiniband/hw/hfi1/
index 7750a9c..1df7da4 100644
--- a/drivers/infiniband/hw/hfi1/file_ops.c
+++ b/drivers/infiniband/hw/hfi1/file_ops.c
@@ -763,11 +763,11 @@ static int complete_subctxt(struct hfi1_filedata *fd)
        }
 
        if (ret) {
-               hfi1_rcd_put(fd->uctxt);
-               fd->uctxt = NULL;
                spin_lock_irqsave(&fd->dd->uctxt_lock, flags);
                __clear_bit(fd->subctxt, fd->uctxt->in_use_ctxts);
                spin_unlock_irqrestore(&fd->dd->uctxt_lock, flags);
+               hfi1_rcd_put(fd->uctxt);
+               fd->uctxt = NULL;
        }

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