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kernel: sucompat: increase reliability, commonize and micro-optimize tiann #2656

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On plain ARMv8.0 devices (A53,A57,A73), strncpy_from_user_nofault() sometimes
fails to copy `filename_user` string correctly. This breaks su ofc, breaking
some apps like Termux (Play Store ver), ZArchiver and Root Explorer.

Apply the susfs patch

This does NOT seem to affect newer ARMv8.2+ CPUs (A75/A76 and newer)

My speculation? ARMv8.0 has weak speculation :)

here we replace `ksu_strncpy_from_user_nofault` with ksu_strncpy_from_user_retry:
- ksu_strncpy_from_user_nofault as fast-path copy
- fallback to access_ok to validate the pointer + strncpy_from_user
- manual null-termination just in case, as strncpy_from_user_nofault also does it
- remove that memset, seems useless as it is an strncpy, not strncat

basically, we retry on pagefualt

for usercopies, its not like were doing
    memset(dest, 0, sizeof(dest));
    strncat(dest, var, bytes);

that memset seems unneeded. instead we use strncpy itself to do proper
error and oob check and null term it after.

as for optimizations
- just return early if unauthorized
- commonized logic
- reduced duplication

Tested on:
- ARMv8.0 A73.a53, A57.a53, A53.a53
- ARMv8.2 A76.a55

Stale: tiann #2656

Co-authored-by: backslashxx <118538522+backslashxx@users.noreply.github.com>
Co-authored-by: ShirkNeko <109797057+ShirkNeko@users.noreply.github.com>
Co-authored-by: rsuntk <rsuntk@yukiprjkt.my.id>
Signed-off-by: ShirkNeko <109797057+ShirkNeko@users.noreply.github.com>
This commit is contained in:
ShirkNeko
2025-09-25 19:41:26 +08:00
parent a85ce2bc35
commit dd1eb98963
5 changed files with 84 additions and 223 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
kernel/Makefile
View File

@@ -122,9 +122,6 @@ ccflags-y += -DKSU_COMPAT_HAS_SELINUX_STATE
endif
# Handle optional backports
ifeq ($(shell grep -q "strncpy_from_user_nofault" $(srctree)/include/linux/uaccess.h; echo $$?),0)
ccflags-y += -DKSU_OPTIONAL_STRNCPY
endif
ifeq ($(shell grep -q "ssize_t kernel_read" $(srctree)/fs/read_write.c; echo $$?),0)
ccflags-y += -DKSU_OPTIONAL_KERNEL_READ
endif

91
kernel/kernel_compat.c
View File

@@ -145,80 +145,12 @@ 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) || defined(KSU_OPTIONAL_STRNCPY)
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
long ksu_strncpy_from_user_retry(char *dst, const void __user *unsafe_addr,
long count)
{
long ret;
ret = ksu_strncpy_from_user_nofault(dst, unsafe_addr, count);
if (likely(ret >= 0))
return ret;
// we faulted! fallback to slow path
if (unlikely(!ksu_access_ok(unsafe_addr, count))) {
#ifdef CONFIG_KSU_DEBUG
pr_err("%s: faulted!\n", __func__);
#endif
return -EFAULT;
}
// why we don't do like how strncpy_from_user_nofault?
ret = strncpy_from_user(dst, unsafe_addr, count);
if (ret >= count) {
ret = count;
dst[ret - 1] = '\0';
} else if (likely(ret >= 0)) {
ret++;
}
return ret;
}
long ksu_copy_from_user_nofault(void *dst, const void __user *src, size_t size)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
return copy_from_user_nofault(dst, src, size);
#elif LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0)
return probe_user_read(dst, src, size);
#else
// https://elixir.bootlin.com/linux/v5.8/source/mm/maccess.c#L205
long ret = -EFAULT;
@@ -238,3 +170,22 @@ long ksu_copy_from_user_nofault(void *dst, const void __user *src, size_t size)
return 0;
#endif
}
/*
* ksu_copy_from_user_retry
* try nofault copy first, if it fails, try with plain
* paramters are the same as copy_from_user
* 0 = success
* + hot since this is reused on sucompat
*/
__attribute__((hot))
long ksu_copy_from_user_retry(void *to,
const void __user *from, unsigned long count)
{
long ret = ksu_copy_from_user_nofault(to, from, count);
if (likely(!ret))
return ret;
// we faulted! fallback to slow path
return copy_from_user(to, from, count);
}

24
kernel/kernel_compat.h
View File

@@ -57,13 +57,6 @@ static inline __maybe_unused size_t list_count_nodes(const struct list_head *hea
#endif
#endif
extern long ksu_strncpy_from_user_nofault(char *dst,
const void __user *unsafe_addr,
long count);
extern long ksu_strncpy_from_user_retry(char *dst,
const void __user *unsafe_addr,
long count);
#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0) || \
defined(CONFIG_IS_HW_HISI) || \
defined(CONFIG_KSU_ALLOWLIST_WORKAROUND)
@@ -78,22 +71,7 @@ extern ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count,
extern ssize_t ksu_kernel_write_compat(struct file *p, const void *buf,
size_t count, loff_t *pos);
extern long ksu_copy_from_user_nofault(void *dst, const void __user *src, size_t size);
/*
* ksu_copy_from_user_retry
* try nofault copy first, if it fails, try with plain
* paramters are the same as copy_from_user
* 0 = success
*/
static long ksu_copy_from_user_retry(void *to,
const void __user *from, unsigned long count)
{
long ret = ksu_copy_from_user_nofault(to, from, count);
if (likely(!ret))
return ret;
// we faulted! fallback to slow path
return copy_from_user(to, from, count);
}
extern long ksu_copy_from_user_retry(void *to, const void __user *from, unsigned long count);
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 0, 0)
#define ksu_access_ok(addr, size) access_ok(addr, size)

2
kernel/ksud.c
View File

@@ -636,7 +636,7 @@ static int ksu_execve_ksud_common(const char __user *filename_user,
if (!filename_user)
return 0;
len = ksu_strncpy_from_user_nofault(path, filename_user, 32);
len = ksu_copy_from_user_retry(path, filename_user, 32);
if (len <= 0)
return 0;

187
kernel/sucompat.c
View File

@@ -55,38 +55,83 @@ static inline char __user *ksud_user_path(void)
return userspace_stack_buffer(ksud_path, sizeof(ksud_path));
}
int ksu_handle_faccessat(int *dfd, const char __user **filename_user, int *mode,
int *__unused_flags)
// every little bit helps here
__attribute__((hot, no_stack_protector))
static __always_inline bool is_su_allowed(const void *ptr_to_check)
{
#ifndef CONFIG_KSU_KPROBES_HOOK
if (!ksu_sucompat_hook_state) {
return 0;
return false;
}
#endif
#ifndef CONFIG_KSU_SUSFS_SUS_SU
if (!ksu_is_allow_uid(current_uid().val)) {
if (likely(!ksu_is_allow_uid(current_uid().val)))
return false;
#endif
if (unlikely(!ptr_to_check))
return false;
return true;
}
static int ksu_sucompat_user_common(const char __user **filename_user,
const char *syscall_name,
const bool escalate)
{
char path[sizeof(su)]; // sizeof includes nullterm already!
if (ksu_copy_from_user_retry(path, *filename_user, sizeof(path)))
return 0;
}
#endif
#ifdef CONFIG_KSU_SUSFS_SUS_SU
char path[sizeof(su) + 1] = {0};
#else
char path[sizeof(su) + 1];
memset(path, 0, sizeof(path));
#endif
ksu_strncpy_from_user_nofault(path, *filename_user, sizeof(path));
path[sizeof(path) - 1] = '\0';
if (unlikely(!memcmp(path, su, sizeof(su)))) {
pr_info("faccessat su->sh!\n");
if (memcmp(path, su, sizeof(su)))
return 0;
if (escalate) {
pr_info("%s su found\n", syscall_name);
*filename_user = ksud_user_path();
escape_to_root(); // escalate !!
} else {
pr_info("%s su->sh!\n", syscall_name);
*filename_user = sh_user_path();
}
return 0;
}
// sys_faccessat
int ksu_handle_faccessat(int *dfd, const char __user **filename_user, int *mode,
int *__unused_flags)
{
if (!is_su_allowed((const void *)filename_user))
return 0;
return ksu_sucompat_user_common(filename_user, "faccessat", false);
}
// sys_newfstatat, sys_fstat64
int ksu_handle_stat(int *dfd, const char __user **filename_user, int *flags)
{
if (!is_su_allowed((const void *)filename_user))
return 0;
return ksu_sucompat_user_common(filename_user, "newfstatat", false);
}
// sys_execve, compat_sys_execve
int ksu_handle_execve_sucompat(int *fd, const char __user **filename_user,
void *__never_use_argv, void *__never_use_envp,
int *__never_use_flags)
{
if (!is_su_allowed((const void *)filename_user))
return 0;
return ksu_sucompat_user_common(filename_user, "sys_execve", true);
}
#if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 1, 0) && defined(CONFIG_KSU_SUSFS_SUS_SU)
struct filename* susfs_ksu_handle_stat(int *dfd, const char __user **filename_user, int *flags) {
struct filename *name = getname_flags(*filename_user, getname_statx_lookup_flags(*flags), NULL);
@@ -106,56 +151,6 @@ struct filename* susfs_ksu_handle_stat(int *dfd, const char __user **filename_us
}
#endif
int ksu_handle_stat(int *dfd, const char __user **filename_user, int *flags)
{
#ifndef CONFIG_KSU_KPROBES_HOOK
if (!ksu_sucompat_hook_state) {
return 0;
}
#endif
#ifndef CONFIG_KSU_SUSFS_SUS_SU
if (!ksu_is_allow_uid(current_uid().val)) {
return 0;
}
#endif
if (unlikely(!filename_user)) {
return 0;
}
#ifdef CONFIG_KSU_SUSFS_SUS_SU
char path[sizeof(su) + 1] = {0};
#else
char path[sizeof(su) + 1];
memset(path, 0, sizeof(path));
#endif
// Remove this later!! we use syscall hook, so this will never happen!!!!!
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 18, 0) && 0
// it becomes a `struct filename *` after 5.18
// https://elixir.bootlin.com/linux/v5.18/source/fs/stat.c#L216
const char sh[] = SH_PATH;
struct filename *filename = *((struct filename **)filename_user);
if (IS_ERR(filename)) {
return 0;
}
if (likely(memcmp(filename->name, su, sizeof(su))))
return 0;
pr_info("vfs_statx su->sh!\n");
memcpy((void *)filename->name, sh, sizeof(sh));
#else
ksu_strncpy_from_user_nofault(path, *filename_user, sizeof(path));
if (unlikely(!memcmp(path, su, sizeof(su)))) {
pr_info("newfstatat su->sh!\n");
*filename_user = sh_user_path();
}
#endif
return 0;
}
// the call from execve_handler_pre won't provided correct value for __never_use_argument, use them after fix execve_handler_pre, keeping them for consistence for manually patched code
int ksu_handle_execveat_sucompat(int *fd, struct filename **filename_ptr,
void *__never_use_argv, void *__never_use_envp,
@@ -163,13 +158,7 @@ int ksu_handle_execveat_sucompat(int *fd, struct filename **filename_ptr,
{
struct filename *filename;
#ifndef CONFIG_KSU_KPROBES_HOOK
if (!ksu_sucompat_hook_state) {
return 0;
}
#endif
if (unlikely(!filename_ptr))
if (!is_su_allowed((const void *)filename_ptr))
return 0;
filename = *filename_ptr;
@@ -180,11 +169,6 @@ int ksu_handle_execveat_sucompat(int *fd, struct filename **filename_ptr,
if (likely(memcmp(filename->name, su, sizeof(su))))
return 0;
#ifndef CONFIG_KSU_SUSFS_SUS_SU
if (!ksu_is_allow_uid(current_uid().val))
return 0;
#endif
pr_info("do_execveat_common su found\n");
memcpy((void *)filename->name, ksud_path, sizeof(ksud_path));
@@ -193,55 +177,6 @@ int ksu_handle_execveat_sucompat(int *fd, struct filename **filename_ptr,
return 0;
}
int ksu_handle_execve_sucompat(int *fd, const char __user **filename_user,
void *__never_use_argv, void *__never_use_envp,
int *__never_use_flags)
{
//const char su[] = SU_PATH;
#ifdef CONFIG_KSU_SUSFS_SUS_SU
char path[sizeof(su) + 1] = {0};
#else
char path[sizeof(su) + 1];
#endif
#ifndef CONFIG_KSU_KPROBES_HOOK
if (!ksu_sucompat_hook_state) {
return 0;
}
#endif
if (unlikely(!filename_user))
return 0;
/*
* nofault variant fails silently due to pagefault_disable
* some cpus dont really have that good speculative execution
* access_ok to substitute set_fs, we check if pointer is accessible
*/
if (!ksu_access_ok(*filename_user, sizeof(path)))
return 0;
// success = returns number of bytes and should be less than path
long len = strncpy_from_user(path, *filename_user, sizeof(path));
if (len <= 0 || len > sizeof(path))
return 0;
// strncpy_from_user_nofault does this too
path[sizeof(path) - 1] = '\0';
if (likely(memcmp(path, su, sizeof(su))))
return 0;
if (!ksu_is_allow_uid(current_uid().val))
return 0;
pr_info("sys_execve su found\n");
*filename_user = ksud_user_path();
escape_to_root();
return 0;
}
// dummified
int ksu_handle_devpts(struct inode *inode)
{