linux-kernel - RE: [PATCH 2/3] scsi: qedf: do not touch __user pointer in qedf_dbg_debug_cmd

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Message-ID: <2938f701ba56419e861f1bb410831862@AcuMS.aculab.com>
Date:   Fri, 28 Jul 2023 15:26:11 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Oleksandr Natalenko' <oleksandr@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        Saurav Kashyap <skashyap@...vell.com>,
        Johannes Thumshirn <Johannes.Thumshirn@....com>,
        "GR-QLogic-Storage-Upstream@...vell.com" 
        <GR-QLogic-Storage-Upstream@...vell.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jozef Bacik <jobacik@...hat.com>,
        Laurence Oberman <loberman@...hat.com>,
        "Rob Evers" <revers@...hat.com>
Subject: RE: [PATCH 2/3] scsi: qedf: do not touch __user pointer in
 qedf_dbg_debug_cmd_read() directly

From: Oleksandr Natalenko
> Sent: 28 July 2023 07:58
> 
> The qedf_dbg_debug_cmd_read() function invokes sprintf()
> directly on a __user pointer, which may crash the kernel.
                                      ^^^ will

> 
> Avoid doing that by using a small on-stack buffer for sprintf()
> and then calling simple_read_from_buffer() which does a proper
> copy_to_user() call.
...
> diff --git a/drivers/scsi/qedf/qedf_debugfs.c b/drivers/scsi/qedf/qedf_debugfs.c
> index 4d1b99569d490..f910af0029a2c 100644
> --- a/drivers/scsi/qedf/qedf_debugfs.c
> +++ b/drivers/scsi/qedf/qedf_debugfs.c
> @@ -138,15 +138,14 @@ qedf_dbg_debug_cmd_read(struct file *filp, char __user *buffer, size_t count,
>  			loff_t *ppos)
>  {
>  	int cnt;
> +	char cbuf[35];

Why 35?
I pick a multiple of 8 that if 'enough.

>  	struct qedf_dbg_ctx *qedf_dbg =
>  				(struct qedf_dbg_ctx *)filp->private_data;
> 
>  	QEDF_INFO(qedf_dbg, QEDF_LOG_DEBUGFS, "debug mask=0x%x\n", qedf_debug);
> -	cnt = sprintf(buffer, "debug mask = 0x%x\n", qedf_debug);
> +	cnt = sprintf(cbuf, "debug mask = 0x%x\n", qedf_debug);

Use scnprintf() to be sure it doesn't overflow.
Much safer if someone does a quick update or copies the code.

	David

> 
> -	cnt = min_t(int, count, cnt - *ppos);
> -	*ppos += cnt;
> -	return cnt;
> +	return simple_read_from_buffer(buffer, count, ppos, cbuf, cnt);
>  }
> 
>  static ssize_t
> --
> 2.41.0

-
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