[RFC PATCH 3/3] scsi: qedf: do not touch __user pointer in qedf_dbg_fp_int_cmd_read() directly

[Oleksandr Natalenko <oleksandr@redhat.com>]

The qedf_dbg_fp_int_cmd_read() function invokes sprintf()
directly on a __user pointer, which may crash the kernel.

Avoid doing that by vmalloc()'ating a buffer for scnprintf()
and then calling simple_read_from_buffer() which does a proper
copy_to_user() call.

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
---
 drivers/scsi/qedf/qedf_dbg.h     |  2 ++
 drivers/scsi/qedf/qedf_debugfs.c | 21 +++++++++++++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/qedf/qedf_dbg.h b/drivers/scsi/qedf/qedf_dbg.h
index f4d81127239eb..5ec2b817c694a 100644
--- a/drivers/scsi/qedf/qedf_dbg.h
+++ b/drivers/scsi/qedf/qedf_dbg.h
@@ -59,6 +59,8 @@ extern uint qedf_debug;
 #define QEDF_LOG_NOTICE	0x40000000	/* Notice logs */
 #define QEDF_LOG_WARN		0x80000000	/* Warning logs */
 
+#define QEDF_DEBUGFS_LOG_LEN (2 * PAGE_SIZE)
+
 /* Debug context structure */
 struct qedf_dbg_ctx {
 	unsigned int host_no;
diff --git a/drivers/scsi/qedf/qedf_debugfs.c b/drivers/scsi/qedf/qedf_debugfs.c
index f910af0029a2c..6db996b73fe39 100644
--- a/drivers/scsi/qedf/qedf_debugfs.c
+++ b/drivers/scsi/qedf/qedf_debugfs.c
@@ -8,6 +8,7 @@
 #include <linux/uaccess.h>
 #include <linux/debugfs.h>
 #include <linux/module.h>
+#include <linux/vmalloc.h>
 
 #include "qedf.h"
 #include "qedf_dbg.h"
@@ -98,7 +99,9 @@ static ssize_t
 qedf_dbg_fp_int_cmd_read(struct file *filp, char __user *buffer, size_t count,
 			 loff_t *ppos)
 {
+	ssize_t ret;
 	size_t cnt = 0;
+	char *cbuf;
 	int id;
 	struct qedf_fastpath *fp = NULL;
 	struct qedf_dbg_ctx *qedf_dbg =
@@ -108,19 +111,25 @@ qedf_dbg_fp_int_cmd_read(struct file *filp, char __user *buffer, size_t count,
 
 	QEDF_INFO(qedf_dbg, QEDF_LOG_DEBUGFS, "entered\n");
 
-	cnt = sprintf(buffer, "\nFastpath I/O completions\n\n");
+	cbuf = vmalloc(QEDF_DEBUGFS_LOG_LEN);
+	if (!cbuf)
+		return 0;
+
+	cnt += scnprintf(cbuf + cnt, QEDF_DEBUGFS_LOG_LEN - cnt, "\nFastpath I/O completions\n\n");
 
 	for (id = 0; id < qedf->num_queues; id++) {
 		fp = &(qedf->fp_array[id]);
 		if (fp->sb_id == QEDF_SB_ID_NULL)
 			continue;
-		cnt += sprintf((buffer + cnt), "#%d: %lu\n", id,
-			       fp->completions);
+		cnt += scnprintf(cbuf + cnt, QEDF_DEBUGFS_LOG_LEN - cnt,
+				 "#%d: %lu\n", id, fp->completions);
 	}
 
-	cnt = min_t(int, count, cnt - *ppos);
-	*ppos += cnt;
-	return cnt;
+	ret = simple_read_from_buffer(buffer, count, ppos, cbuf, cnt);
+
+	vfree(cbuf);
+
+	return ret;
 }
 
 static ssize_t
-- 
2.41.0