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@gmail.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

On Thu, Jun 15, 2023 at 06:05:04PM +0000, Azeem Shaikh wrote:
> 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@gmail.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

On 6/21/23 21:10, Kees Cook wrote:
> On Thu, Jun 15, 2023 at 06:05:04PM +0000, Azeem Shaikh wrote:
>> 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@gmail.com>
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 

Acked-by: Shuah Khan <skhan@linuxfoundation.org>

thanks,
-- Shuah