[PATCH v3] uml: Replace strlcpy with strscpy

[PATCH v3] uml: Replace strlcpy with strscpy

[Azeem Shaikh]

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>
---
v1: https://lore.kernel.org/all/20230530164004.986750-1-azeemshaikh38@gmail.com/
v2: https://lore.kernel.org/all/20230606182410.3976487-1-azeemshaikh38@gmail.com/

Changes from v1 - added strscpy declaration. v1 does not build.
Changes from v2 - removed Reported-By: and Closes: tag from commit log.

 arch/um/include/shared/user.h          | 1 +
 arch/um/os-Linux/drivers/tuntap_user.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index bda66e5a9d4e..0347a190429c 100644
--- 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 53eb3d508645..2284e9c1cbbb 100644
--- 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",
-- 
2.41.0.rc0.172.g3f132b7071-goog

Re: [PATCH v3] uml: Replace strlcpy with strscpy

[Kees Cook]

On Wed, 14 Jun 2023 00:36:04 +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().
> No return values were used, so direct replacement is safe.
> 
> [...]

Build tested with "ARCH=um".

Applied to for-next/hardening, thanks!

[1/1] uml: Replace strlcpy with strscpy
      https://git.kernel.org/kees/c/e1ca49d0291a

-- 
Kees Cook