kernel: fix probe_kernel_read failed to read user addr

kernel/kernel_compat.c

@@ -131,3 +131,43 @@ ssize_t ksu_kernel_write_compat(struct file *p, const void *buf, size_t count,
 	return result;
 #endif
 }
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
+long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
+				   long count)
+{
+	return strncpy_from_user_nofault(dst, unsafe_addr, count);
+}
+#elif LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0)
+long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
+				   long count)
+{
+	return strncpy_from_unsafe_user(dst, unsafe_addr, count);
+}
+#else
+// Copied from: https://elixir.bootlin.com/linux/v4.9.337/source/mm/maccess.c#L201
+long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
+				   long count)
+{
+	mm_segment_t old_fs = get_fs();
+	long ret;
+
+	if (unlikely(count <= 0))
+		return 0;
+
+	set_fs(USER_DS);
+	pagefault_disable();
+	ret = strncpy_from_user(dst, unsafe_addr, count);
+	pagefault_enable();
+	set_fs(old_fs);
+
+	if (ret >= count) {
+		ret = count;
+		dst[ret - 1] = '\0';
+	} else if (ret > 0) {
+		ret++;
+	}
+
+	return ret;
+}
+#endif

kernel/kernel_compat.h

@@ -6,21 +6,20 @@
 #include "linux/version.h"
 #include "linux/uaccess.h"
 
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
+extern long ksu_strncpy_from_user_nofault(char *dst,
-#define ksu_strncpy_from_user_nofault strncpy_from_user_nofault
+					  const void __user *unsafe_addr,
-#elif LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0)
+					  long count);
-#define ksu_strncpy_from_user_nofault strncpy_from_unsafe_user
-#else
-#define ksu_strncpy_from_user_nofault probe_kernel_read
-#endif
 
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
 extern struct key *init_session_keyring;
 #endif
 
 extern void ksu_android_ns_fs_check();
-extern struct file *ksu_filp_open_compat(const char *filename, int flags, umode_t mode);
+extern struct file *ksu_filp_open_compat(const char *filename, int flags,
-extern ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count, loff_t *pos);
+					 umode_t mode);
-extern ssize_t ksu_kernel_write_compat(struct file *p, const void *buf, size_t count, loff_t *pos);
+extern ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count,
+				      loff_t *pos);
+extern ssize_t ksu_kernel_write_compat(struct file *p, const void *buf,
+				       size_t count, loff_t *pos);
 
 #endif