[PATCH] init/version.c: Replace strlcpy with strscpy

[PATCH] init/version.c: 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().

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>
---
 init/version.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/init/version.c b/init/version.c
index f117921811b4..94c96f6fbfe6 100644
--- a/init/version.c
+++ b/init/version.c
@@ -21,10 +21,10 @@ static int __init early_hostname(char *arg)
 {
 	size_t bufsize = sizeof(init_uts_ns.name.nodename);
 	size_t maxlen  = bufsize - 1;
-	size_t arglen;
+	ssize_t arglen;

-	arglen = strlcpy(init_uts_ns.name.nodename, arg, bufsize);
-	if (arglen > maxlen) {
+	arglen = strscpy(init_uts_ns.name.nodename, arg, bufsize);
+	if (arglen < 0) {
 		pr_warn("hostname parameter exceeds %zd characters and will be truncated",
 			maxlen);
 	}
--
2.41.0.255.g8b1d071c50-goog

Re: [PATCH] init/version.c: Replace strlcpy with strscpy

[Justin Stitt]

On Wed, Aug 30, 2023 at 12:29 PM Azeem Shaikh <azeemshaikh38@gmail.com> 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).

Great patch! This is similar to [1] which aims to eradicate strncpy.

>
> [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: Justin Stitt <justinstitt@google.com>

> ---
>  init/version.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/init/version.c b/init/version.c
> index f117921811b4..94c96f6fbfe6 100644
> --- a/init/version.c
> +++ b/init/version.c
> @@ -21,10 +21,10 @@ static int __init early_hostname(char *arg)
>  {
>         size_t bufsize = sizeof(init_uts_ns.name.nodename);
>         size_t maxlen  = bufsize - 1;
> -       size_t arglen;
> +       ssize_t arglen;
>
> -       arglen = strlcpy(init_uts_ns.name.nodename, arg, bufsize);
> -       if (arglen > maxlen) {
> +       arglen = strscpy(init_uts_ns.name.nodename, arg, bufsize);
> +       if (arglen < 0) {
>                 pr_warn("hostname parameter exceeds %zd characters and will be truncated",
>                         maxlen);
>         }
> --
> 2.41.0.255.g8b1d071c50-goog
>
>

[1]: https://github.com/KSPP/linux/issues/90

Re: [PATCH] init/version.c: Replace strlcpy with strscpy

[Kees Cook]

On Wed, Aug 30, 2023 at 04:08:06PM +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>
> ---
>  init/version.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/init/version.c b/init/version.c
> index f117921811b4..94c96f6fbfe6 100644
> --- a/init/version.c
> +++ b/init/version.c
> @@ -21,10 +21,10 @@ static int __init early_hostname(char *arg)
>  {
>  	size_t bufsize = sizeof(init_uts_ns.name.nodename);
>  	size_t maxlen  = bufsize - 1;
> -	size_t arglen;
> +	ssize_t arglen;
> 
> -	arglen = strlcpy(init_uts_ns.name.nodename, arg, bufsize);
> -	if (arglen > maxlen) {
> +	arglen = strscpy(init_uts_ns.name.nodename, arg, bufsize);
> +	if (arglen < 0) {

nitpick: this is no longer "length of arg", it's the length of the
destination string. Regardless:

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

>  		pr_warn("hostname parameter exceeds %zd characters and will be truncated",
>  			maxlen);
>  	}
> --
> 2.41.0.255.g8b1d071c50-goog
> 
> 

-- 
Kees Cook

Re: [PATCH] init/version.c: Replace strlcpy with strscpy

[Kees Cook]

On Wed, 30 Aug 2023 16:08:06 +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().
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] init/version.c: Replace strlcpy with strscpy
      https://git.kernel.org/kees/c/ec23bc09c1c0

Take care,

-- 
Kees Cook