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

[Oleksandr Natalenko <oleksandr@redhat.com>]

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.

Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
---
 drivers/scsi/qedf/qedf_debugfs.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

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");
 
-	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