kernel/fork: factor out replacing the current MM exe_file

Let's factor the main logic out into replace_mm_exe_file(), such that
all mm->exe_file logic is contained in kernel/fork.c.

While at it, perform some simple cleanups that are possible now that
we're simplifying the individual functions.

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7ca22e6..48c6fa9 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2581,6 +2581,7 @@ extern int mm_take_all_locks(struct mm_struct *mm);
 extern void mm_drop_all_locks(struct mm_struct *mm);
 
 extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
+extern int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
 extern struct file *get_mm_exe_file(struct mm_struct *mm);
 extern struct file *get_task_exe_file(struct task_struct *task);
 

diff --git a/kernel/fork.c b/kernel/fork.c
index 44f4c2d..f4ac883 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1148,9 +1148,7 @@ void mmput_async(struct mm_struct *mm)
  *
  * Main users are mmput() and sys_execve(). Callers prevent concurrent
  * invocations: in mmput() nobody alive left, in execve task is single
- * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
- * mm->exe_file, but does so without using set_mm_exe_file() in order
- * to avoid the need for any locks.
+ * threaded.
  */
 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 {
@@ -1170,6 +1168,46 @@ void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
                fput(old_exe_file);
 }
 
+/**
+ * replace_mm_exe_file - replace a reference to the mm's executable file
+ *
+ * This changes mm's executable file (shown as symlink /proc/[pid]/exe),
+ * dealing with concurrent invocation and without grabbing the mmap lock in
+ * write mode.
+ *
+ * Main user is sys_prctl(PR_SET_MM_MAP/EXE_FILE).
+ */
+int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
+{
+       struct vm_area_struct *vma;
+       struct file *old_exe_file;
+       int ret = 0;
+
+       /* Forbid mm->exe_file change if old file still mapped. */
+       old_exe_file = get_mm_exe_file(mm);
+       if (old_exe_file) {
+               mmap_read_lock(mm);
+               for (vma = mm->mmap; vma && !ret; vma = vma->vm_next) {
+                       if (!vma->vm_file)
+                               continue;
+                       if (path_equal(&vma->vm_file->f_path,
+                                      &old_exe_file->f_path))
+                               ret = -EBUSY;
+               }
+               mmap_read_unlock(mm);
+               fput(old_exe_file);
+               if (ret)
+                       return ret;
+       }
+
+       /* set the new file, lockless */
+       get_file(new_exe_file);
+       old_exe_file = xchg(&mm->exe_file, new_exe_file);
+       if (old_exe_file)
+               fput(old_exe_file);
+       return 0;
+}
+
 /**
  * get_mm_exe_file - acquire a reference to the mm's executable file
  *

diff --git a/kernel/sys.c b/kernel/sys.c
index ef1a78f..30c12e5 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1846,7 +1846,6 @@ SYSCALL_DEFINE1(umask, int, mask)
 static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
 {
        struct fd exe;
-       struct file *old_exe, *exe_file;
        struct inode *inode;
        int err;
 
@@ -1869,40 +1868,10 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
        if (err)
                goto exit;
 
-       /*
-        * Forbid mm->exe_file change if old file still mapped.
-        */
-       exe_file = get_mm_exe_file(mm);
-       err = -EBUSY;
-       if (exe_file) {
-               struct vm_area_struct *vma;
-
-               mmap_read_lock(mm);
-               for (vma = mm->mmap; vma; vma = vma->vm_next) {
-                       if (!vma->vm_file)
-                               continue;
-                       if (path_equal(&vma->vm_file->f_path,
-                                      &exe_file->f_path))
-                               goto exit_err;
-               }
-
-               mmap_read_unlock(mm);
-               fput(exe_file);
-       }
-
-       err = 0;
-       /* set the new file, lockless */
-       get_file(exe.file);
-       old_exe = xchg(&mm->exe_file, exe.file);
-       if (old_exe)
-               fput(old_exe);
+       err = replace_mm_exe_file(mm, exe.file);
 exit:
        fdput(exe);
        return err;
-exit_err:
-       mmap_read_unlock(mm);
-       fput(exe_file);
-       goto exit;
 }
 
 /*