kernel: handle backports

It is a common thing on the scene to backport things, so this breaks kernel versioning
assumptions. As for those, we scan and check kernel source.

The following are backportable:
 - path_umount:
	context: tiann#1464 (comment)
	apply: xiaomi-sdm678/android_kernel_xiaomi_mojito@2d51422

 - strncpy_from_user_nofault
 	for 5.4, apply: torvalds/linux@bd88bb5
 	for 4.x, apply: xiaomi-sdm678/android_kernel_xiaomi_mojito@424e21f
 	for any failures, check dependency chain of gregkh/linux@f43434e

 - kernel_read / kernel_write
 	< 4.14, backport chain, tested on 4.9
 	torvalds/linux@e13ec93
	torvalds/linux@bdd1d2d
	torvalds/linux@c41fbad
	torvalds/linux@ac452ac

- hint, `curl $url.patch | git am`

Signed-off-by: backslashxx <[email protected]>

Author: backslashxx

kernel/Makefile

@@ -57,10 +57,28 @@ ccflags-y += -DEXPECTED_SIZE=$(KSU_EXPECTED_SIZE)
 ccflags-y += -DEXPECTED_HASH=\"$(KSU_EXPECTED_HASH)\"
 
 ifeq ($(shell grep -q "int path_umount" $(srctree)/fs/namespace.c; echo $$?),0)
-ccflags-y += -DKSU_UMOUNT
-else
-$(info -- Did you know you can backport path_umount to fs/namespace.c from 5.9?)
-$(info -- Read: https://kernelsu.org/guide/how-to-integrate-for-non-gki.html#how-to-backport-path-umount)
+$(info -- KernelSU/compat: path_umount found)
+ccflags-y += -DKSU_HAS_PATH_UMOUNT
+endif
+
+ifeq ($(shell grep -q "strncpy_from_user_nofault" $(srctree)/include/linux/uaccess.h; echo $$?),0)
+$(info -- KernelSU/compat: strncpy_from_user_nofault found)
+ccflags-y += -DKSU_STRNCPY_FROM_USER_NOFAULT
+endif
+
+ifeq ($(shell grep -q "strncpy_from_unsafe_user" $(srctree)/include/linux/uaccess.h; echo $$?),0)
+$(info -- KernelSU/compat: strncpy_from_unsafe_user found)
+ccflags-y += -DKSU_STRNCPY_FROM_UNSAFE_USER
+endif
+
+ifeq ($(shell grep -q "ssize_t kernel_read" $(srctree)/fs/read_write.c; echo $$?),0)
+$(info -- KernelSU/compat: newer kernel_read found)
+ccflags-y += -DKSU_NEW_KERNEL_READ
+endif
+
+ifeq ($(shell grep "ssize_t kernel_write" $(srctree)/fs/read_write.c | grep -q "const void" ; echo $$?),0)
+$(info -- KernelSU/compat: newer kernel_write found)
+ccflags-y += -DKSU_NEW_KERNEL_WRITE
 endif
 
 ccflags-y += -Wno-implicit-function-declaration -Wno-strict-prototypes -Wno-int-conversion -Wno-gcc-compat

kernel/kernel_compat.c

@@ -107,7 +107,7 @@ struct file *ksu_filp_open_compat(const char *filename, int flags, umode_t mode)
 ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count,
 			       loff_t *pos)
 {
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0) || defined(KSU_NEW_KERNEL_READ)
 	return kernel_read(p, buf, count, pos);
 #else
 	loff_t offset = pos ? *pos : 0;
@@ -122,7 +122,7 @@ ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count,
 ssize_t ksu_kernel_write_compat(struct file *p, const void *buf, size_t count,
 				loff_t *pos)
 {
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0) || defined(KSU_NEW_KERNEL_WRITE)
 	return kernel_write(p, buf, count, pos);
 #else
 	loff_t offset = pos ? *pos : 0;
@@ -134,20 +134,19 @@ ssize_t ksu_kernel_write_compat(struct file *p, const void *buf, size_t count,
 #endif
 }
 
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0) || defined(KSU_STRNCPY_FROM_USER_NOFAULT)
 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)
+#elif LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0) || defined(KSU_STRNCPY_FROM_UNSAFE_USER)
 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
+#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)
 {