linux-hardening - [PATCH v3] usbip: usbip_host: Replace strlcpy with strscpy

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Message-ID: <20230615180504.401169-1-azeemshaikh38@gmail.com>
Date:   Thu, 15 Jun 2023 18:05:04 +0000
From:   Azeem Shaikh <azeemshaikh38@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>
Cc:     linux-hardening@...r.kernel.org,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        Hongren Zheng <i@...ithal.me>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] usbip: usbip_host: 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 sizeof(dest).

[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>
---
v3:
 * Removed declaration of @len to fix build failures in v2.

v2:
 * https://lore.kernel.org/all/20230614141026.2113749-1-azeemshaikh38@gmail.com/
 * Use "< 0" instead of "== -E2BIG".

v1: 
 * https://lore.kernel.org/all/20230613004402.3540432-1-azeemshaikh38@gmail.com/

 drivers/usb/usbip/stub_main.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/usb/usbip/stub_main.c b/drivers/usb/usbip/stub_main.c
index e8c3131a8543..0a6624d37929 100644
--- a/drivers/usb/usbip/stub_main.c
+++ b/drivers/usb/usbip/stub_main.c
@@ -167,15 +167,13 @@ static ssize_t match_busid_show(struct device_driver *drv, char *buf)
 static ssize_t match_busid_store(struct device_driver *dev, const char *buf,
 				 size_t count)
 {
-	int len;
 	char busid[BUSID_SIZE];
 
 	if (count < 5)
 		return -EINVAL;
 
 	/* busid needs to include \0 termination */
-	len = strlcpy(busid, buf + 4, BUSID_SIZE);
-	if (sizeof(busid) <= len)
+	if (strscpy(busid, buf + 4, BUSID_SIZE) < 0)
 		return -EINVAL;
 
 	if (!strncmp(buf, "add ", 4)) {
-- 
2.41.0.162.gfafddb0af9-goog