sound: oss: off by one bug

The problem is that in the original code sound_nblocks could go up to 1024
which would be an array overflow.

This was found with a static checker and has been compile tested only.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

sound/oss/dev_table.c

@@ -67,14 +67,15 @@ int sound_install_audiodrv(int vers, char *name, struct audio_driver *driver,
 		return -(EBUSY);
 	}
 	d = (struct audio_driver *) (sound_mem_blocks[sound_nblocks] = vmalloc(sizeof(struct audio_driver)));
-
-	if (sound_nblocks < 1024)
-		sound_nblocks++;
+	sound_nblocks++;
+	if (sound_nblocks >= MAX_MEM_BLOCKS)
+		sound_nblocks = MAX_MEM_BLOCKS - 1;
 
 	op = (struct audio_operations *) (sound_mem_blocks[sound_nblocks] = vmalloc(sizeof(struct audio_operations)));
+	sound_nblocks++;
+	if (sound_nblocks >= MAX_MEM_BLOCKS)
+		sound_nblocks = MAX_MEM_BLOCKS - 1;
 
-	if (sound_nblocks < 1024)
-		sound_nblocks++;
 	if (d == NULL || op == NULL) {
 		printk(KERN_ERR "Sound: Can't allocate driver for (%s)\n", name);
 		sound_unload_audiodev(num);
@@ -128,9 +129,10 @@ int sound_install_mixer(int vers, char *name, struct mixer_operations *driver,
 	   until you unload sound! */
 
 	op = (struct mixer_operations *) (sound_mem_blocks[sound_nblocks] = vmalloc(sizeof(struct mixer_operations)));
+	sound_nblocks++;
+	if (sound_nblocks >= MAX_MEM_BLOCKS)
+		sound_nblocks = MAX_MEM_BLOCKS - 1;
 
-	if (sound_nblocks < 1024)
-		sound_nblocks++;
 	if (op == NULL) {
 		printk(KERN_ERR "Sound: Can't allocate mixer driver for (%s)\n", name);
 		return -ENOMEM;

sound/oss/sound_config.h

@@ -142,4 +142,6 @@ static inline int translate_mode(struct file *file)
 #define TIMER_ARMED	121234
 #define TIMER_NOT_ARMED	1
 
+#define MAX_MEM_BLOCKS 1024
+
 #endif

sound/oss/soundcard.c

@@ -56,7 +56,7 @@
 /*
  * Table for permanently allocated memory (used when unloading the module)
  */
-void *          sound_mem_blocks[1024];
+void *          sound_mem_blocks[MAX_MEM_BLOCKS];
 int             sound_nblocks = 0;
 
 /* Persistent DMA buffers */
@@ -574,7 +574,7 @@ static int __init oss_init(void)
 				      NULL, "%s%d", dev_list[i].name, j);
 	}
 
-	if (sound_nblocks >= 1024)
+	if (sound_nblocks >= MAX_MEM_BLOCKS - 1)
 		printk(KERN_ERR "Sound warning: Deallocation table was too small.\n");
 
 	return 0;