[PATCH 2/3] scsi: qedf: do not touch __user pointer in qedf_dbg_debug_cmd_read() directly

[Oleksandr Natalenko]

The qedf_dbg_debug_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.")
Link: https://lore.kernel.org/lkml/20230724120241.40495-1-oleksandr@xxxxxxxxxx/
Link: https://lore.kernel.org/linux-scsi/20230726101236.11922-1-skashyap@xxxxxxxxxxx/
Cc: Saurav Kashyap <skashyap@xxxxxxxxxxx>
Cc: Rob Evers <revers@xxxxxxxxxx>
Cc: Johannes Thumshirn <Johannes.Thumshirn@xxxxxxx>
Cc: Jozef Bacik <jobacik@xxxxxxxxxx>
Cc: Laurence Oberman <loberman@xxxxxxxxxx>
Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxx>
Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
Cc: GR-QLogic-Storage-Upstream@xxxxxxxxxxx
Cc: linux-scsi@xxxxxxxxxxxxxxx
Tested-by: Laurence Oberman <loberman@xxxxxxxxxx>
Signed-off-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxx>
---
 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 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];
 	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);
 
-	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