[PATCH v2] accessibility: speakup: refactor deprecated strncpy

[Justin Stitt]

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

Let's refactor this function to just use synth_write().

Link: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings[1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@xxxxxxxxxxxxxxx
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
---
Changes from v1 -> v2:
- refactor synth_direct_store (thanks Kees)
- rebase onto 3669558bdf354cd352be955ef2764cde6a9bf5ec
- Link to v1: https://lore.kernel.org/all/20230824-strncpy-drivers-accessibility-speakup-kobjects-c-v1-1-3a1ef1221e90@xxxxxxxxxx/
---
 drivers/accessibility/speakup/kobjects.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/drivers/accessibility/speakup/kobjects.c b/drivers/accessibility/speakup/kobjects.c
index a7522d409802..0dfdb6608e02 100644
--- a/drivers/accessibility/speakup/kobjects.c
+++ b/drivers/accessibility/speakup/kobjects.c
@@ -413,27 +413,24 @@ static ssize_t synth_direct_store(struct kobject *kobj,
 				  struct kobj_attribute *attr,
 				  const char *buf, size_t count)
 {
-	u_char tmp[256];
-	int len;
-	int bytes;
-	const char *ptr = buf;
+	char *unescaped;
 	unsigned long flags;
 
 	if (!synth)
 		return -EPERM;
 
-	len = strlen(buf);
+	unescaped = kstrdup(buf, GFP_KERNEL);
+	if (!unescaped)
+		return -ENOMEM;
+
+	string_unescape_any_inplace(unescaped);
+
 	spin_lock_irqsave(&speakup_info.spinlock, flags);
-	while (len > 0) {
-		bytes = min_t(size_t, len, 250);
-		strncpy(tmp, ptr, bytes);
-		tmp[bytes] = '\0';
-		string_unescape_any_inplace(tmp);
-		synth_printf("%s", tmp);
-		ptr += bytes;
-		len -= bytes;
-	}
+	synth_write(unescaped, strlen(unescaped));
 	spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+
+	kfree(unescaped);
+
 	return count;
 }
 

---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230824-strncpy-drivers-accessibility-speakup-kobjects-c-4009e7df0936

Best regards,
--
Justin Stitt <justinstitt@xxxxxxxxxx>