accessibility: speakup: refactor deprecated strncpy

`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
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20230918-strncpy-drivers-accessibility-speakup-kobjects-c-v2-1-d5b1976c5dbf@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/accessibility/speakup/kobjects.c b/drivers/accessibility/speakup/kobjects.c
index a7522d4..0dfdb66 100644 (file)
--- 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;
 }