2023-06-14 01:07:14

by Azeem Shaikh

Subject: [PATCH v3] 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 <[email protected]>
---
v1: https://lore.kernel.org/all/[email protected]/
v2: https://lore.kernel.org/all/[email protected]/

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

2023-06-20 21:17:33

by Kees Cook

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

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