uml: 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().
No return values were used, so direct replacement is safe.

[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>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230614003604.1021205-1-azeemshaikh38@gmail.com

diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index bda66e5..0347a19 100644 (file)
--- a/arch/um/include/shared/user.h
+++ b/arch/um/include/shared/user.h
@@ -52,6 +52,7 @@ static inline int printk(const char *fmt, ...)
 extern int in_aton(char *str);
 extern size_t strlcpy(char *, const char *, size_t);
 extern size_t strlcat(char *, const char *, size_t);
+extern size_t strscpy(char *, const char *, size_t);
 
 /* Copied from linux/compiler-gcc.h since we can't include it directly */
 #define barrier() __asm__ __volatile__("": : :"memory")

diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index 53eb3d5..2284e9c 100644 (file)
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -146,7 +146,7 @@ static int tuntap_open(void *data)
                }
                memset(&ifr, 0, sizeof(ifr));
                ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
-               strlcpy(ifr.ifr_name, pri->dev_name, sizeof(ifr.ifr_name));
+               strscpy(ifr.ifr_name, pri->dev_name, sizeof(ifr.ifr_name));
                if (ioctl(pri->fd, TUNSETIFF, &ifr) < 0) {
                        err = -errno;
                        printk(UM_KERN_ERR "TUNSETIFF failed, errno = %d\n",