Commit 35d7bdc8 authored by David Hildenbrand's avatar David Hildenbrand
Browse files

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: default avatarChristian Brauner <christian.brauner@ubuntu.com>
Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
parent 42be8b42

include/linux/mm.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

kernel/fork.c

+41 −3
Original line number Diff line number Diff line
@@ -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

 *

kernel/sys.c

+1 −32
Original line number Diff line number Diff line
@@ -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;

}



/*