Add qemu scripts to debug the null ptr dereference bug

.gitignore

@@ -92,4 +92,6 @@ extra_certificates
 signing_key.priv
 signing_key.x509
 x509.genkey
-*.mod
+*.mod
+root_fs
+root.img

Makefile

@@ -6,6 +6,18 @@ build_dir = /lib/modules/$(kernel_version)/build
 
 all:
 	$(MAKE) -C $(build_dir) M=$(PWD) modules
+.PHONY: load
+load:
+	insmod ksudoku.ko
+	insmod simple.ko
+.PHONY: unload
+unload:
+	rmmod simple.ko
+	rmmod ksudoku.ko
+
+.PHONY: send
+send:
+	@echo "670008010020060000000030000201000006480001700000000009004500000000000300003400802" > /sys/kernel/ksudoku/simple/matrix
 clean:
 	$(MAKE) -C $(build_dir) M=$(PWD) clean
 	rm *~

ksudoku.c

@@ -1,4 +1,4 @@
-/*
+/**
  * KSudoku subsystem for Linux kernel to solve sudoku with different
  * algorithms.
  * Copyright (C) 2020 Sameer Rahmani <lxsameer@gnu.org>
@@ -117,7 +117,9 @@ static ssize_t matrix_show(struct ksudoku *s,
                            struct ksudoku_attribute *attr,
                            char *buf)
 {
-        return sprintf(buf, "%s", s->matrix);
+        if (s->matrix)
+                return sprintf(buf, "NULL");
+        return sprintf(buf, "%s\n", s->matrix);
 }
 
 static ssize_t matrix_store(struct ksudoku *s,
@@ -126,14 +128,28 @@ static ssize_t matrix_store(struct ksudoku *s,
                             size_t len)
 {
         int status = atomic_read(&s->status);
+        char *p = (char *) buf;
+        int i, j, retval;
+
+        printk(KERN_INFO "len: %ld.\n", len);
 
         if (status == KSUDOKU_BUSY)
                 return -EBUSY;
 
-        if (len != 81)
+        if (len != 82)
                 return -EIO;
 
         strncpy(s->matrix, buf, len);
+        for (i = 0; i < 9; i++) {
+                for (j = 0; j < 9; j++) {
+                        char g = (char) *p;
+                        retval = kstrtoint(&g, 10 , &s->matrix_array[i][j]);
+
+                        if (!retval)
+                                return -EINVAL;
+                        p++;
+                }
+        }
         return len;
 }
 
@@ -189,6 +205,7 @@ struct ksudoku *ksudoku_create_sudoku(const char *name)
 }
 EXPORT_SYMBOL_GPL(ksudoku_create_sudoku);
 
+
 /**
  * ksudoku_destroy_ksudoku - destroys the given ksudoku instance.
  * @sudoku: Pointer to a ksudoku instance to destroy.
@@ -199,9 +216,49 @@ void ksudoku_destroy_ksudoku(struct ksudoku *sudoku)
 }
 EXPORT_SYMBOL_GPL(ksudoku_destroy_ksudoku);
 
+
+/**
+ * ksudoku_is_cell_valid - Checks for a valid value in the given cell
+ * @sudoku: Pointer to a ksudoku instance.
+ * @v: The value to check
+ * @row: the row number of the sudoku table
+ * @col: the column number of the sudoku table
+ */
+bool ksudoku_is_valid_cell(struct ksudoku *s, int v, int row, int col)
+{
+        int i=0;
+        int box_row = 3 * (row / 3);
+        int box_col = 3 * (col / 3);
+        int row1 = (row + 2) % 3;
+        int row2 = (row + 4) % 3;
+        int col1 = (col + 2) % 3;
+        int col2 = (col + 4) % 3;
+
+    /* Check for the value in the given row and column */
+    for (i = 0; i < 9; i++) {
+        if (s->matrix_array[i][col] == v)
+                return false;
+        if (s->matrix_array[row][i] == v)
+                return false;
+    }
+
+    /* Check the remaining four spaces in this sector */
+    if (s->matrix_array[row1 + box_row][col1 + box_col] == v)
+            return false;
+    if (s->matrix_array[row2 + box_row][col1 + box_col] == v)
+            return false;
+    if (s->matrix_array[row1 + box_row][col2 + box_col] == v)
+            return false;
+    if (s->matrix_array[row2 + box_row][col2 + box_col] == v)
+            return false;
+    return true;
+}
+EXPORT_SYMBOL_GPL(ksudoku_is_valid_cell);
+
+
 static int ksudoku_init(void)
 {
-        printk(KERN_ALERT "Init ksudoku subsystem.\n");
+        printk(KERN_INFO "Init ksudoku subsystem.\n");
 
         // kernel_kobj is the kobject related to /sys/kernel
         ksudoku_set = kset_create_and_add("ksudoku", NULL, kernel_kobj);
@@ -209,34 +266,15 @@ static int ksudoku_init(void)
         if (!ksudoku_set)
                 return -ENOMEM;
 
-        printk(KERN_ALERT "Ready to register sudokus.\n");
-        /* sudoku = kmalloc(sizeof (struct ksudoku), GFP_KERNEL); */
-
-        /* atomic_set(&sudoku->status, 0); */
-        /* sudoku->attr_group = &attr_group; */
-
-        /* if (!sudoku) */
-        /*         return -ENOMEM; */
-
-        /* sudoku->kobj = kobject_create_and_add("ksudoku", kernel_kobj); */
-
-        /* if (!&sudoku->kobj) */
-        /*         return -ENOMEM; */
-
-        /* sysfs_result = sysfs_create_group(sudoku->kobj, sudoku->attr_group); */
-
-        /* if (sysfs_result) */
-        /*         kobject_put(sudoku->kobj); */
-
+        printk(KERN_INFO "Ready to register sudokus.\n");
         return 0;
 }
 
 
 static void ksudoku_exit(void)
 {
-        //kobject_put(sudoku->kobj);
         kset_unregister(ksudoku_set);
-        printk(KERN_ALERT "Exit ksudoku.\n");
+        printk(KERN_INFO "Exit ksudoku.\n");
 }
 
 

ksudoku.h

@@ -1,4 +1,4 @@
-/*
+/**
  * KSudoku subsystem for Linux kernel to solve sudoku with different
  * algorithms.
  * Copyright (C) 2020 Sameer Rahmani <lxsameer@gnu.org>
@@ -33,6 +33,7 @@ struct ksudoku {
         struct kobject kobj;
         const struct attribute_group *attr_group;
         char *matrix;
+        int matrix_array[9][9];
         atomic_t status;
 };
 #define to_ksudoku(obj) container_of(obj, struct ksudoku, kobj)
@@ -50,5 +51,6 @@ struct ksudoku_attribute {
 
 extern struct ksudoku *ksudoku_create_sudoku(const char *name);
 extern void ksudoku_destroy_ksudoku(struct ksudoku *sudoku);
+extern bool ksudoku_is_valid_cell(struct ksudoku *sudoku, int v, int row, int col);
 
 #endif

simple.c

@@ -1,4 +1,4 @@
-/*
+/**
  * A simple algorithm to solve sudoku for ksudoku subsystem
  * Copyright (C) 2020 Sameer Rahmani <lxsameer@gnu.org>
  *
@@ -24,6 +24,7 @@
 
 static struct ksudoku *sudoku;
 
+
 static int simple_sudoku_init(void)
 {
 

tools/boot_kernel.sh

@@ -1,10 +1,9 @@
 #! /bin/bash
 
 qemu-system-x86_64 \
-    -kernel /boot/vmlinuz-`uname -r` \
-    -nographic \
-    -append "console=ttyS0 nokaslr init=/bin/bash" \
-    -initrd `pwd`/ram.disk \
-    -m 512 \
-    --enable-kvm \
-    -cpu host
+    -kernel /lib/modules/`uname -r`/build/arch/x86/boot/bzImage \
+    -append "root=/dev/ram init=/init console=ttyS0" \
+    -initrd `pwd`/initrd.img \
+    -nographic -smp 1 -cpu host --enable-kvm\
+    -m 2048 \
+    -drive file=fat:rw:`pwd`

tools/build_initrd.sh

@@ -0,0 +1,6 @@
+#! /bin/bash
+
+
+wget https://www.busybox.net/downloads/busybox-1.31.1.tar.bz2
+tar jxvf busybox-1.31.1.tar.bz2
+cd busybox-1.31.1

tools/create_fs.sh

@@ -1,12 +1,15 @@
 #! /bin/bash
 
-IMG=`pwd`/qemu-image.img
-DIR=`pwd`/mounted_fs
+IMG=`pwd`/root.img
+MOUNT_POINT=`pwd`/mnt
+DIR=./root_fs
 
-qemu-img create $IMG 1g
+
+qemu-img create $IMG 1G
 sudo mkfs.ext2 $IMG
-mkdir $DIR
-sudo mount -o loop $IMG $DIR
-sudo debootstrap --arch amd64 buster $DIR
-sudo umount $DIR
-rmdir $DIR
+mkdir -p $DIR $MOUNT_POINT
+sudo mount -o loop $IMG $MOUNT_POINT
+sudo debootstrap stable $DIR http://ftp.de.debian.org/debian
+sudo mv $DIR/* $MOUNT_POINT/
+sudo umount $MOUNT_POINT
+sudo rm -rf $MOUNT_POINT