Re: [PATCH] ALSA: mixer_oss: Replace deprecated strcpy() with strscpy()

[Takashi Iwai <tiwai@suse.de>]

On Thu, 19 Jun 2025 14:50:04 +0200,
Thorsten Blum wrote:
> 
> On 19. Jun 2025, at 00:49, Al Viro wrote:
> > On Thu, Jun 19, 2025 at 12:36:29AM +0200, Thorsten Blum wrote:
> >> strcpy() is deprecated; use strscpy() instead.
> >> 
> >> No functional changes intended.
> > 
> > Have you actually read the damn thing?  Seriously, look at the uses
> > of 'str' downstream.  The only thing it is ever passed to is strcmp().
> > 
> > In other words, why do we need to copy it anywhere?  What's wrong with
> > having char *str instead of that array and replacing strcpy() with
> > plain and simple pointer assignment?
> 
> I read it, but didn't question whether copying was actually necessary.
> 
> However, it looks like 'ptr->name' can originate from userland (via proc
> file - see the function comment), which could make using 'char *str'
> directly unsafe, unless I'm missing something.
> 
> Something like this would skip one copy while keeping it safe:
> 
> char tmp_str[64];
> char *str;
> 
> strscpy(tmp_str, ptr->name);
> if (!strcmp(tmp_str, "Master"))
> 	str = "Mix";
> else if (!strcmp(tmp_str, "Master Mono"))
> 	str = "Mix Mono";
> else
> 	str = tmp_str;

Al is right, we should optimize it instead.  As it's been already a
string copied to a kernel, and the string is certainly NUL-terminated,
hence there is no need to worry about using the pointer.
It'd be something like:

--- a/sound/core/oss/mixer_oss.c
+++ b/sound/core/oss/mixer_oss.c
@@ -991,7 +991,7 @@ static int snd_mixer_oss_build_input(struct snd_mixer_oss *mixer,
 	struct slot *pslot;
 	struct snd_kcontrol *kctl;
 	struct snd_mixer_oss_slot *rslot;
-	char str[64];	
+	const char *str;
 	
 	/* check if already assigned */
 	if (mixer->slots[ptr->oss_id].get_volume && ! replace_old)
@@ -1014,11 +1014,11 @@ static int snd_mixer_oss_build_input(struct snd_mixer_oss *mixer,
 			
 		if (kctl->info(kctl, uinfo))
 			return 0;
-		strcpy(str, ptr->name);
+		str = ptr->name;
 		if (!strcmp(str, "Master"))
-			strcpy(str, "Mix");
-		if (!strcmp(str, "Master Mono"))
-			strcpy(str, "Mix Mono");
+			str = "Mix";
+		else if (!strcmp(str, "Master Mono"))
+			str = "Mix Mono";
 		slot.capture_item = 0;
 		if (!strcmp(uinfo->value.enumerated.name, str)) {
 			slot.present |= SNDRV_MIXER_OSS_PRESENT_CAPTURE;


thanks,

Takashi