linux-hardening - [PATCH v2] usb: gadget: function: printer: Replace strlcpy with strscpy

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Date:   Thu, 15 Jun 2023 18:03:18 +0000
From:   Azeem Shaikh <azeemshaikh38@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     linux-hardening@...r.kernel.org,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Albert Briscoe <albertsbriscoe@...il.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: [PATCH v2] usb: gadget: function: printer: Replace strlcpy with strscpy

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().

Direct replacement is safe here since return value of -errno
is used to check for truncation instead of PAGE_SIZE.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
---
v2:
 * Use "< 1" instead of "== -E2BIG".
 * Update commit log to say PAGE_SIZE instead of sizeof(dest).

v1:
 * https://lore.kernel.org/all/20230613004341.3540325-1-azeemshaikh38@gmail.com/

 drivers/usb/gadget/function/f_printer.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index 28db3e336e7d..b91425611969 100644
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -1211,8 +1211,8 @@ static ssize_t f_printer_opts_pnp_string_show(struct config_item *item,
 	if (!opts->pnp_string)
 		goto unlock;
 
-	result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
-	if (result >= PAGE_SIZE) {
+	result = strscpy(page, opts->pnp_string, PAGE_SIZE);
+	if (result < 1) {
 		result = PAGE_SIZE;
 	} else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
 		page[result++] = '\n';
-- 
2.41.0.162.gfafddb0af9-goog