soundwire: fix bug in sdw_add_element_group_count found by syzkaller

The original implementation caused an out-of-bounds memory access
in the sdw_add_element_group_count for-loop when i == num.

for (i = 0; i <= num; i++) {
    if (rate == group->rates[i] && lane == group->lanes[i])
        ...

To fix this error, the function now checks for existing rate/lane
entries in the group(a function parameter) using a for-loop before
adding them.

No functional changes apart from this fix.

Fixes: 9026118 ("soundwire: Add generic bandwidth allocation algorithm")
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Baoli.Zhang <baoli.zhang@linux.intel.com>
Link: https://patch.msgid.link/20260506055039.3751028-2-baoli.zhang@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Baoli.Zhang

drivers/soundwire/generic_bandwidth_allocation.c

@@ -299,39 +299,36 @@ static int sdw_add_element_group_count(struct sdw_group *group,
 	int num = group->count;
 	int i;
 
-	for (i = 0; i <= num; i++) {
+	for (i = 0; i < num; i++) {
 		if (rate == group->rates[i] && lane == group->lanes[i])
-			break;
-
-		if (i != num)
-			continue;
-
-		if (group->count >= group->max_size) {
-			unsigned int *rates;
-			unsigned int *lanes;
+			return 0;
+	}
 
-			group->max_size += 1;
-			rates = krealloc(group->rates,
-					 (sizeof(int) * group->max_size),
-					 GFP_KERNEL);
-			if (!rates)
-				return -ENOMEM;
+	if (group->count >= group->max_size) {
+		unsigned int *rates;
+		unsigned int *lanes;
 
-			group->rates = rates;
+		group->max_size += 1;
+		rates = krealloc(group->rates,
+				 (sizeof(int) * group->max_size),
+				 GFP_KERNEL);
+		if (!rates)
+			return -ENOMEM;
 
-			lanes = krealloc(group->lanes,
-					 (sizeof(int) * group->max_size),
-					 GFP_KERNEL);
-			if (!lanes)
-				return -ENOMEM;
+		group->rates = rates;
 
-			group->lanes = lanes;
-		}
+		lanes = krealloc(group->lanes,
+				 (sizeof(int) * group->max_size),
+				 GFP_KERNEL);
+		if (!lanes)
+			return -ENOMEM;
 
-		group->rates[group->count] = rate;
-		group->lanes[group->count++] = lane;
+		group->lanes = lanes;
 	}
 
+	group->rates[group->count] = rate;
+	group->lanes[group->count++] = lane;
+
 	return 0;
 }