linux-kernel - [PATCH 09/12] usb: mon_stat: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <20231213164246.1021885-10-lee@kernel.org>
Date:   Wed, 13 Dec 2023 16:42:38 +0000
From:   Lee Jones <lee@...nel.org>
To:     lee@...nel.org, gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: [PATCH 09/12] usb: mon_stat: Replace snprintf() with the safer scnprintf() variant

There is a general misunderstanding amongst engineers that {v}snprintf()
returns the length of the data *actually* encoded into the destination
array.  However, as per the C99 standard {v}snprintf() really returns
the length of the data that *would have been* written if there were
enough space for it.  This misunderstanding has led to buffer-overruns
in the past.  It's generally considered safer to use the {v}scnprintf()
variants in their place (or even sprintf() in simple cases).  So let's
do that.

Link: https://lwn.net/Articles/69419/
Link: https://github.com/KSPP/linux/issues/105
Signed-off-by: Lee Jones <lee@...nel.org>
---
 drivers/usb/mon/mon_stat.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/mon/mon_stat.c b/drivers/usb/mon/mon_stat.c
index 98ab0cc473d67..3c23805ab1a44 100644
--- a/drivers/usb/mon/mon_stat.c
+++ b/drivers/usb/mon/mon_stat.c
@@ -35,9 +35,9 @@ static int mon_stat_open(struct inode *inode, struct file *file)
 
 	mbus = inode->i_private;
 
-	sp->slen = snprintf(sp->str, STAT_BUF_SIZE,
-	    "nreaders %d events %u text_lost %u\n",
-	    mbus->nreaders, mbus->cnt_events, mbus->cnt_text_lost);
+	sp->slen = scnprintf(sp->str, STAT_BUF_SIZE,
+			     "nreaders %d events %u text_lost %u\n",
+			     mbus->nreaders, mbus->cnt_events, mbus->cnt_text_lost);
 
 	file->private_data = sp;
 	return 0;
-- 
2.43.0.472.g3155946c3a-goog