linux-hardening - [PATCH v3] kobject: Replace strlcpy with strscpy

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Date:   Wed, 30 Aug 2023 20:20:21 +0000
From:   Azeem Shaikh <azeemshaikh38@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>
Cc:     linux-hardening@...r.kernel.org,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] kobject: 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().

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@...il.com>
---
v3:
 * Fixed weird indentation.

v2:
 * Updated error message to remove @len which is errno now.
 * https://lore.kernel.org/all/20230830150136.3798414-1-azeemshaikh38@gmail.com/

v1:
 * https://lore.kernel.org/all/20230703180528.3709258-1-azeemshaikh38@gmail.com/

 lib/kobject_uevent.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 7c44b7ae4c5c..032d81b959f0 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -254,10 +254,10 @@ static int init_uevent_argv(struct kobj_uevent_env *env, const char *subsystem)
 	int buffer_size = sizeof(env->buf) - env->buflen;
 	int len;

-	len = strlcpy(&env->buf[env->buflen], subsystem, buffer_size);
-	if (len >= buffer_size) {
-		pr_warn("init_uevent_argv: buffer size of %d too small, needed %d\n",
-			buffer_size, len);
+	len = strscpy(&env->buf[env->buflen], subsystem, buffer_size);
+	if (len < 0) {
+		pr_warn("init_uevent_argv: insufficient buffer space "
+			"(%u left) for %s\n", buffer_size, subsystem);
 		return -ENOMEM;
 	}

--
2.42.0.rc2.253.gd59a3bf2b4-goog