linux-kernel - [PATCH v2] usb: fotg210-hcd: delete an incorrect bounds test

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Date:   Wed, 13 Dec 2023 16:22:43 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Lee Jones <lee@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: [PATCH v2] usb: fotg210-hcd: delete an incorrect bounds test

Here "temp" is the number of characters that we have written and "size"
is the size of the buffer.  The intent was clearly to say that if we have
written to the end of the buffer then stop.

However, for that to work the comparison should have been done on the
original "size" value instead of the "size -= temp" value.  Not only
will that not trigger when we want to, but there is a small chance that
it will trigger incorrectly before we want it to and we break from the
loop slightly earlier than intended.

This code was recently changed from using snprintf() to scnprintf().  With
snprintf() we likely would have continued looping and passed a negative
size parameter to snprintf().  This would have triggered an annoying
WARN().  Now that we have converted to scnprintf() "size" will never
drop below 1 and there is no real need for this test.  We could change
the condition to "if (temp <= 1) goto done;" but just deleting the test
is cleanest.

Fixes: 7d50195f6c50 ("usb: host: Faraday fotg210-hcd driver")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
Reviewed-by: Lee Jones <lee@...nel.org>
---
v2: Use the correct Fixes tag.  Add Reviewed-by tags.

 drivers/usb/fotg210/fotg210-hcd.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/usb/fotg210/fotg210-hcd.c b/drivers/usb/fotg210/fotg210-hcd.c
index b2f8b53cc8ef..8c5aaf860635 100644
--- a/drivers/usb/fotg210/fotg210-hcd.c
+++ b/drivers/usb/fotg210/fotg210-hcd.c
@@ -426,8 +426,6 @@ static void qh_lines(struct fotg210_hcd *fotg210, struct fotg210_qh *qh,
 				td->urb);
 		size -= temp;
 		next += temp;
-		if (temp == size)
-			goto done;
 	}

 	temp = scnprintf(next, size, "\n");
@@ -435,7 +433,6 @@ static void qh_lines(struct fotg210_hcd *fotg210, struct fotg210_qh *qh,
 	size -= temp;
 	next += temp;

-done:
 	*sizep = size;
 	*nextp = next;
 }
-- 
2.42.0