cleanup get_file_rcu() which is changed from 6.7

define our own rather than using kernel's rcu-protected implementation.
it's guaranteed that our usecases are in atomic context or task_lock.

Signed-off-by: shenping.matt <shenping.matt@bytedance.com>

Author: shenping-bd

driver/LKM/include/smith_hook.h

@@ -46,10 +46,6 @@
 #include <linux/kmod.h>
 #include <linux/dcache.h>
 
-#ifndef get_file_rcu
-#define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count)
-#endif
-
 #if LINUX_VERSION_CODE < KERNEL_VERSION(3, 1, 0)
 #define __ARG_PLACEHOLDER_1 0,
 #define config_enabled(cfg) _config_enabled(cfg)

driver/LKM/src/smith_hook.c

@@ -457,6 +457,9 @@ static char *smith_d_path(const struct path *path, char *buf, int buflen)
     return name;
 }
 
+/* only inc f_count when it's not 0 to avoid races upon exe_file */
+#define smith_get_file(x) atomic_long_inc_not_zero(&(x)->f_count)
+
 /*
  * query task's executable image file, with mmap lock avoided, just because
  * mmput() could lead resched() (since it's calling might_sleep() interally)
@@ -478,14 +481,8 @@ static struct file *smith_get_task_exe_file(struct task_struct *task)
     task_lock(task);
     if (task->mm && task->mm->exe_file) {
         exe = task->mm->exe_file;
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 1, 0)
-        if (!get_file_rcu(exe))
-            exe = NULL;
-#else
-        /* only inc f_count when it's not 0 to avoid races upon exe_file */
-        if (!atomic_long_inc_not_zero(&exe->f_count))
+        if (!smith_get_file(exe))
             exe = NULL;
-#endif
     }
     task_unlock(task);
 
@@ -2955,7 +2952,7 @@ static int mprotect_pre_handler(struct kprobe *p, struct pt_regs *regs)
             rcu_read_lock();
             if (!IS_ERR_OR_NULL(vma->vm_mm)) {
                 if (!IS_ERR_OR_NULL(&vma->vm_mm->exe_file)) {
-                    if (get_file_rcu(vma->vm_mm->exe_file)) {
+                    if (smith_get_file(vma->vm_mm->exe_file)) {
                         file_buf = smith_kzalloc(PATH_MAX, GFP_ATOMIC);
                         file_path = smith_d_path(&vma->vm_mm->exe_file->f_path, file_buf, PATH_MAX);
                         smith_fput(vma->vm_mm->exe_file);
@@ -2967,9 +2964,8 @@ static int mprotect_pre_handler(struct kprobe *p, struct pt_regs *regs)
             }
 
             if (!IS_ERR_OR_NULL(vma->vm_file)) {
-                if (get_file_rcu(vma->vm_file)) {
-                    vm_file_buff =
-                            smith_kzalloc(PATH_MAX, GFP_ATOMIC);
+                if (smith_get_file(vma->vm_file)) {
+                    vm_file_buff = smith_kzalloc(PATH_MAX, GFP_ATOMIC);
                     vm_file_path = smith_d_path(&vma->vm_file->f_path, vm_file_buff, PATH_MAX);
                     smith_fput(vma->vm_file);
                 }