Re: [PATCH] mvsas:Fix possible NULL pointer deference in mvs_dev_found_notify

Re: [PATCH] mvsas:Fix possible NULL pointer deference in mvs_dev_found_notify

[Luis de Bethencourt]

On 01/07/16 18:43, Nicholas Krause wrote:
> This adds properly checking after the call to mvs_find_dev_mvi
> due to this function being able to return a NULL pointer and if
> this does arise we will deference it in mvs_alloc_dev due to
> this function never checking if a NULL pointer is given as
> it's input argument.
> v2 - Fix NULL pointer deferenece in error path by calling
> spin_unlock_irqrestore on the now NULL pointer, as returned
> by mvs_find_dev_mvi.

Hi Nicholas,

You mention v2 here but this is [PATCH] and not [PATCH v2]. Is this
the first version of the patch or second?

> 
> Signed-off-by: Nicholas Krause <xerofoify@gmail.com>
> ---

If the "v2 -" comments are part of the review and not of the git commit
message it is better to place it here. Between the "---" and the diff.

This is because when the maintainer applies the patch this section will
be truncated, and it won't show in the git log.

>  drivers/scsi/mvsas/mv_sas.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/scsi/mvsas/mv_sas.c b/drivers/scsi/mvsas/mv_sas.c
> index 83cd3ea..74f3954 100644
> --- a/drivers/scsi/mvsas/mv_sas.c
> +++ b/drivers/scsi/mvsas/mv_sas.c
> @@ -1191,6 +1191,10 @@ int mvs_dev_found_notify(struct domain_device *dev, int lock)
>  	struct mvs_device *mvi_device;
>  
>  	mvi = mvs_find_dev_mvi(dev);
> +	if (!mvi) {
> +		res = -1;
> +		goto found_null;
> +	}
>  
>  	if (lock)
>  		spin_lock_irqsave(&mvi->lock, flags);
> @@ -1230,6 +1234,7 @@ int mvs_dev_found_notify(struct domain_device *dev, int lock)
>  found_out:
>  	if (lock)
>  		spin_unlock_irqrestore(&mvi->lock, flags);
> +found_null:
>  	return res;
>  }
>  
> 

If the goto is just going to return, why not do a return directly instead?

if (!mvi)
    return -1;

Thanks for the patch,
Luis

Re: [PATCH] mvsas:Fix possible NULL pointer deference in mvs_dev_found_notify

[Valdis.Kletnieks]

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On Wed, 09 Mar 2016 22:33:47 +0200, Dāvis Mosāns said:

> About whether mvs_find_dev_mvi can return NULL it looks like it's possible,
> but I'm not sure if it practically happens. I guess it did hence patch.

Or the "bug" was found by incorrect code inspection.  Nick has a history
of submitting patches that are for either non-existent problems or
don't deal with with the issue correctly - bad enough that he's not
allowed to post to the linux-kernel list.

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Re: [PATCH] mvsas:Fix possible NULL pointer deference in mvs_dev_found_notify

[Dāvis Mosāns]

2016-03-09 15:58 GMT+02:00 Nicholas Krause <xerofoify@gmail.com>:
> This adds properly checking after the call to mvs_find_dev_mvi
> due to this function being able to return a NULL pointer and if
> this does arise we will deference it in mvs_alloc_dev due to
> this function never checking if a NULL pointer is given as
> it's input argument.
>
> Signed-off-by: Nicholas Krause <xerofoify@gmail.com>
> ---
>  drivers/scsi/mvsas/mv_sas.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/scsi/mvsas/mv_sas.c b/drivers/scsi/mvsas/mv_sas.c
> index 83cd3ea..7afb248 100644
> --- a/drivers/scsi/mvsas/mv_sas.c
> +++ b/drivers/scsi/mvsas/mv_sas.c
> @@ -1191,6 +1191,10 @@ int mvs_dev_found_notify(struct domain_device *dev, int lock)
>         struct mvs_device *mvi_device;
>
>         mvi = mvs_find_dev_mvi(dev);
> +       if (!mvi) {
> +               res = -1;
> +               goto found_out;
> +       }
>
>         if (lock)
>                 spin_lock_irqsave(&mvi->lock, flags);
> --
> 2.5.0
>

It doesn't look right,
if mvi will be NULL and lock will be set then at

found_out:
    if (lock)
        spin_unlock_irqrestore(&mvi->lock, flags);

there will be mvi dereference, besides spin_lock_irqsave wasn't even called.
And without this patch dereference would happen on mvi->lock which is
before use in mvs_alloc_dev

About whether mvs_find_dev_mvi can return NULL it looks like it's possible,
but I'm not sure if it practically happens. I guess it did hence patch.