1 files changed, 118 insertions, 8 deletions

diff --git a/fs/open.c b/fs/open.c
index b47aab39c057..3cac0bda46df 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -573,13 +573,15 @@ SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
 {
         struct path path;
         int error = -EINVAL;
-        int follow;
+        int lookup_flags;
 
-        if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
+        if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
                 goto out;
 
-        follow = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
-        error = user_path_at(dfd, filename, follow, &path);
+        lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
+        if (flag & AT_EMPTY_PATH)
+                lookup_flags |= LOOKUP_EMPTY;
+        error = user_path_at(dfd, filename, lookup_flags, &path);
         if (error)
                 goto out;
         error = mnt_want_write(path.mnt);
@@ -669,11 +671,16 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
                                         int (*open)(struct inode *, struct file *),
                                         const struct cred *cred)
 {
+        static const struct file_operations empty_fops = {};
         struct inode *inode;
         int error;
 
         f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
                                 FMODE_PREAD | FMODE_PWRITE;
+
+        if (unlikely(f->f_flags & O_PATH))
+                f->f_mode = FMODE_PATH;
+
         inode = dentry->d_inode;
         if (f->f_mode & FMODE_WRITE) {
                 error = __get_file_write_access(inode, mnt);
@@ -687,9 +694,15 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
         f->f_path.dentry = dentry;
         f->f_path.mnt = mnt;
         f->f_pos = 0;
-        f->f_op = fops_get(inode->i_fop);
         file_sb_list_add(f, inode->i_sb);
 
+        if (unlikely(f->f_mode & FMODE_PATH)) {
+                f->f_op = &empty_fops;
+                return f;
+        }
+
+        f->f_op = fops_get(inode->i_fop);
+
         error = security_dentry_open(f, cred);
         if (error)
                 goto cleanup_all;
@@ -890,15 +903,110 @@ void fd_install(unsigned int fd, struct file *file)
 
 EXPORT_SYMBOL(fd_install);
 
+static inline int build_open_flags(int flags, int mode, struct open_flags *op)
+{
+        int lookup_flags = 0;
+        int acc_mode;
+
+        if (!(flags & O_CREAT))
+                mode = 0;
+        op->mode = mode;
+
+        /* Must never be set by userspace */
+        flags &= ~FMODE_NONOTIFY;
+
+        /*
+         * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
+         * check for O_DSYNC if the need any syncing at all we enforce it's
+         * always set instead of having to deal with possibly weird behaviour
+         * for malicious applications setting only __O_SYNC.
+         */
+        if (flags & __O_SYNC)
+                flags |= O_DSYNC;
+
+        /*
+         * If we have O_PATH in the open flag. Then we
+         * cannot have anything other than the below set of flags
+         */
+        if (flags & O_PATH) {
+                flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
+                acc_mode = 0;
+        } else {
+                acc_mode = MAY_OPEN | ACC_MODE(flags);
+        }
+
+        op->open_flag = flags;
+
+        /* O_TRUNC implies we need access checks for write permissions */
+        if (flags & O_TRUNC)
+                acc_mode |= MAY_WRITE;
+
+        /* Allow the LSM permission hook to distinguish append
+           access from general write access. */
+        if (flags & O_APPEND)
+                acc_mode |= MAY_APPEND;
+
+        op->acc_mode = acc_mode;
+
+        op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
+
+        if (flags & O_CREAT) {
+                op->intent |= LOOKUP_CREATE;
+                if (flags & O_EXCL)
+                        op->intent |= LOOKUP_EXCL;
+        }
+
+        if (flags & O_DIRECTORY)
+                lookup_flags |= LOOKUP_DIRECTORY;
+        if (!(flags & O_NOFOLLOW))
+                lookup_flags |= LOOKUP_FOLLOW;
+        return lookup_flags;
+}
+
+/**
+ * filp_open - open file and return file pointer
+ *
+ * @filename:   path to open
+ * @flags:      open flags as per the open(2) second argument
+ * @mode:       mode for the new file if O_CREAT is set, else ignored
+ *
+ * This is the helper to open a file from kernelspace if you really
+ * have to.  But in generally you should not do this, so please move
+ * along, nothing to see here..
+ */
+struct file *filp_open(const char *filename, int flags, int mode)
+{
+        struct open_flags op;
+        int lookup = build_open_flags(flags, mode, &op);
+        return do_filp_open(AT_FDCWD, filename, &op, lookup);
+}
+EXPORT_SYMBOL(filp_open);
+
+struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
+                            const char *filename, int flags)
+{
+        struct open_flags op;
+        int lookup = build_open_flags(flags, 0, &op);
+        if (flags & O_CREAT)
+                return ERR_PTR(-EINVAL);
+        if (!filename && (flags & O_DIRECTORY))
+                if (!dentry->d_inode->i_op->lookup)
+                        return ERR_PTR(-ENOTDIR);
+        return do_file_open_root(dentry, mnt, filename, &op, lookup);
+}
+EXPORT_SYMBOL(file_open_root);
+
 long do_sys_open(int dfd, const char __user *filename, int flags, int mode)
 {
+        struct open_flags op;
+        int lookup = build_open_flags(flags, mode, &op);
         char *tmp = getname(filename);
         int fd = PTR_ERR(tmp);
 
         if (!IS_ERR(tmp)) {
                 fd = get_unused_fd_flags(flags);
                 if (fd >= 0) {
-                        struct file *f = do_filp_open(dfd, tmp, flags, mode, 0);
+                        struct file *f = do_filp_open(dfd, tmp, &op, lookup);
                         if (IS_ERR(f)) {
                                 put_unused_fd(fd);
                                 fd = PTR_ERR(f);
@@ -968,8 +1076,10 @@ int filp_close(struct file *filp, fl_owner_t id)
         if (filp->f_op && filp->f_op->flush)
                 retval = filp->f_op->flush(filp, id);
 
-        dnotify_flush(filp, id);
-        locks_remove_posix(filp, id);
+        if (likely(!(filp->f_mode & FMODE_PATH))) {
+                dnotify_flush(filp, id);
+                locks_remove_posix(filp, id);
+        }
         fput(filp);
         return retval;
 }