kernel: handle backports

Legacy kernel builders have to touch their kernel source code anyway so we
might as well tell them to backport things to achieve some sort of feature
parity.

As for others, 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.

Required:
 - get_cred_rcu:
	context: tiann/KernelSU#2320 (comment)
	apply: torvalds/linux@97d0fb2
	if above conflicts, try: xiaomi-sdm678/android_kernel_xiaomi_mojito@3fbad8b

Optional:
 - path_umount:
	context: tiann/KernelSU#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

@@ -104,47 +104,24 @@ $(info -- KSU_NEXT: modifying 'get_task_cred' function in $(srctree)/kernel/cred
 $(shell sed -i "s/!$(ATOMIC_INC_FUNC)(&((struct cred \*)cred)->usage)/!get_cred_rcu(cred)/g" $(srctree)/kernel/cred.c)
 endif
 
-ifneq ($(shell grep -Eq "^static int can_umount" $(srctree)/fs/namespace.c; echo $$?),0)
-$(info -- KSU_NEXT: adding function 'static int can_umount(const struct path *path, int flags);' to $(srctree)/fs/namespace.c)
-CAN_UMOUNT = static int can_umount(const struct path *path, int flags)\n\
-{\n\t\
-        struct mount *mnt = real_mount(path->mnt);\n\t\
-        if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))\n\t\t\
-                return -EINVAL;\n\t\
-        if (!may_mount())\n\t\t\
-                return -EPERM;\n\t\
-        if (path->dentry != path->mnt->mnt_root)\n\t\t\
-                return -EINVAL;\n\t\
-        if (!check_mnt(mnt))\n\t\t\
-                return -EINVAL;\n\t\
-        if (mnt->mnt.mnt_flags & MNT_LOCKED)\n\t\t\
-                return -EINVAL;\n\t\
-        if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))\n\t\t\
-                return -EPERM;\n\t\
-        return 0;\n\
-}\n
-$(shell sed -i '/^static bool is_mnt_ns_file/i $(CAN_UMOUNT)' $(srctree)/fs/namespace.c;)
+ifeq ($(shell grep -q "int path_umount" $(srctree)/fs/namespace.c; echo $$?),0)
+$(info -- KernelSU/compat: path_umount found)
+ccflags-y += -DKSU_HAS_PATH_UMOUNT
 endif
 
-ifneq ($(shell grep -Eq "^int path_umount" $(srctree)/fs/namespace.c; echo $$?),0)
-$(info -- KSU_NEXT: adding function 'int path_umount(struct path *path, int flags);' to $(srctree)/fs/namespace.c)
-PATH_UMOUNT = int path_umount(struct path *path, int flags)\n\
-{\n\t\
-        struct mount *mnt = real_mount(path->mnt);\n\t\
-        int ret;\n\t\
-        ret = can_umount(path, flags);\n\t\
-        if (!ret)\n\t\t\
-                ret = do_umount(mnt, flags);\n\t\
-        dput(path->dentry);\n\t\
-        mntput_no_expire(mnt);\n\t\
-        return ret;\n\
-}\n
-$(shell sed -i '/^static bool is_mnt_ns_file/i $(PATH_UMOUNT)' $(srctree)/fs/namespace.c;)
+ifeq ($(shell grep -q "strncpy_from_unsafe_user" $(srctree)/include/linux/uaccess.h; echo $$?),0)
+$(info -- KernelSU/compat: strncpy_from_unsafe_user found)
+ccflags-y += -DKSU_STRNCPY_FROM_UNSAFE_USER
 endif
 
-ifneq ($(shell grep -Eq "^int path_umount" $(srctree)/fs/internal.h; echo $$?),0)
-$(shell sed -i '/^extern void __init mnt_init/a int path_umount(struct path *path, int flags);' $(srctree)/fs/internal.h;)
-$(info -- KSU_NEXT: adding 'int path_umount(struct path *path, int flags);' to $(srctree)/fs/internal.h)
+ifeq ($(shell grep -q "ssize_t kernel_read" $(srctree)/fs/read_write.c; echo $$?),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) || defined(KSU_KERNEL_READ)
+#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) || defined(KSU_KERNEL_WRITE)
+#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;
@@ -140,14 +140,13 @@ long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
 {
 	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)
 {