RE: [PATCH 1/3] scsi: qedf: do not touch __user pointer in qedf_dbg_stop_io_on_error_cmd_read() directly

[David Laight <David.Laight@ACULAB.COM>]

From: Oleksandr Natalenko
> Sent: 28 July 2023 07:58
> 
> The qedf_dbg_stop_io_on_error_cmd_read() function invokes sprintf()
> directly on a __user pointer, which may crash the kernel.
> 
> 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.
> 
> Fixes: 61d8658b4a ("scsi: qedf: Add QLogic FastLinQ offload FCoE driver framework.")
...
> diff --git a/drivers/scsi/qedf/qedf_debugfs.c b/drivers/scsi/qedf/qedf_debugfs.c
> index a3ed681c8ce3f..4d1b99569d490 100644
> --- a/drivers/scsi/qedf/qedf_debugfs.c
> +++ b/drivers/scsi/qedf/qedf_debugfs.c
> @@ -185,18 +185,17 @@ qedf_dbg_stop_io_on_error_cmd_read(struct file *filp, char __user *buffer,
>  				   size_t count, loff_t *ppos)
>  {
>  	int cnt;
> +	char cbuf[7];
>  	struct qedf_dbg_ctx *qedf_dbg =
>  				(struct qedf_dbg_ctx *)filp->private_data;
>  	struct qedf_ctx *qedf = container_of(qedf_dbg,
>  	    struct qedf_ctx, dbg_ctx);
> 
>  	QEDF_INFO(qedf_dbg, QEDF_LOG_DEBUGFS, "entered\n");
> -	cnt = sprintf(buffer, "%s\n",
> +	cnt = sprintf(cbuf, "%s\n",
>  	    qedf->stop_io_on_error ? "true" : "false");

You've made cbuf[] exactly just big enough.
If anyone breathes on this code it could overflow.
You really should use scnprintf() for safety.

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

Or just:
	if (gedf->stop_on_error)
		return simple_read_from_buffer(buffer, count, ppos, "true\n", 5);
	return simple_read_from_buffer(buffer, count, ppos, "false\n", 6);

	David

	
>  }
> 
>  static ssize_t
> --
> 2.41.0

-
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