linux-kernel - Re: [PATCH] scsi: sg: fix memory leak in sg_build

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Date:   Mon, 13 Apr 2020 18:15:29 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Li Bin <huawei.libin@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        xiexiuqi@...wei.com
Subject: Re: [PATCH] scsi: sg: fix memory leak in sg_build_indirect

On 2020-04-13 7:32 a.m., Li Bin wrote:
> Fix a memory leak when there have failed, that we should free the pages
> under the condition rem_sz > 0.

May I paraphrase the above:
"Fix a memory leak that occurs when alloc_pages() succeeds several
  times before failing. This condition is noticed when rem_sz > 0."

> 
> Signed-off-by: Li Bin <huawei.libin@...wei.com>
> ---
>   drivers/scsi/sg.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 4e6af592..8441ac5 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1959,8 +1959,12 @@ static long sg_compat_ioctl(struct file *filp, unsigned int cmd_in, unsigned lon

It is the sg_build_indirect() function not sg_compat_ioctl() as suggested
above by git. Can be get a replacement for git :-)

>   			 k, rem_sz));
>   
>   	schp->bufflen = blk_size;
> -	if (rem_sz > 0)	/* must have failed */
> +	if (rem_sz > 0)	{ /* must have failed */
> +		for (i = 0; i < k; i++)
> +			__free_pages(schp->pages[i], order);
> +
>   		return -ENOMEM;

It is easier, and less code, to replace 'return -ENOMEM'; with
'goto out'. Or even simpler:

     if (likely(rem_sz == 0))
	return 0;
out:
      ........

Doug Gilbert

BTW I spotted this one during the sg driver rewrite and fixed it.
Note that this bug and several others like it won't be fixed by
me while the sg driver rewrite is pending.

> +	}
>   	return 0;
>   out:
>   	for (i = 0; i < k; i++)
>