Merge tag 'printk-for-5.10-fixup' of git://git.kernel.org/pub/scm/lin…

…ux/kernel/git/printk/linux

Pull printk fix from Petr Mladek:
 "Prevent overflow in the new lockless ringbuffer"

* tag 'printk-for-5.10-fixup' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk: ringbuffer: Wrong data pointer when appending small string

kernel/printk/printk_ringbuffer.c

@@ -1125,7 +1125,10 @@ static char *data_realloc(struct printk_ringbuffer *rb,
 
 	/* If the data block does not increase, there is nothing to do. */
 	if (head_lpos - next_lpos < DATA_SIZE(data_ring)) {
-		blk = to_block(data_ring, blk_lpos->begin);
+		if (wrapped)
+			blk = to_block(data_ring, 0);
+		else
+			blk = to_block(data_ring, blk_lpos->begin);
 		return &blk->data[0];
 	}