kernel/usermode_driver.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * umd - User mode driver support
   4  */
   5 #include <linux/shmem_fs.h>
   6 #include <linux/pipe_fs_i.h>
   7 #include <linux/mount.h>
   8 #include <linux/fs_struct.h>
   9 #include <linux/task_work.h>
  10 #include <linux/usermode_driver.h>
  11
  12 static struct vfsmount *blob_to_mnt(const void *data, size_t len, const char *name)
  13 {
  14         struct file_system_type *type;
  15         struct vfsmount *mnt;
  16         struct file *file;
  17         ssize_t written;
  18         loff_t pos = 0;
  19
  20         type = get_fs_type("tmpfs");
  21         if (!type)
  22                 return ERR_PTR(-ENODEV);
  23
  24         mnt = kern_mount(type);
  25         put_filesystem(type);
  26         if (IS_ERR(mnt))
  27                 return mnt;
  28
  29         file = file_open_root_mnt(mnt, name, O_CREAT | O_WRONLY, 0700);
  30         if (IS_ERR(file)) {
  31                 kern_unmount(mnt);
  32                 return ERR_CAST(file);
  33         }
  34
  35         written = kernel_write(file, data, len, &pos);
  36         if (written != len) {
  37                 int err = written;
  38                 if (err >= 0)
  39                         err = -ENOMEM;
  40                 filp_close(file, NULL);
  41                 kern_unmount(mnt);
  42                 return ERR_PTR(err);
  43         }
  44
  45         fput(file);
  46
  47         /* Flush delayed fput so exec can open the file read-only */
  48         flush_delayed_fput();
  49         task_work_run();
  50         return mnt;
  51 }
  52
  53 /**
  54  * umd_load_blob - Remember a blob of bytes for fork_usermode_driver
  55  * @info: information about usermode driver
  56  * @data: a blob of bytes that can be executed as a file
  57  * @len:  The lentgh of the blob
  58  *
  59  */
  60 int umd_load_blob(struct umd_info *info, const void *data, size_t len)
  61 {
  62         struct vfsmount *mnt;
  63
  64         if (WARN_ON_ONCE(info->wd.dentry || info->wd.mnt))
  65                 return -EBUSY;
  66
  67         mnt = blob_to_mnt(data, len, info->driver_name);
  68         if (IS_ERR(mnt))
  69                 return PTR_ERR(mnt);
  70
  71         info->wd.mnt = mnt;
  72         info->wd.dentry = mnt->mnt_root;
  73         return 0;
  74 }
  75 EXPORT_SYMBOL_GPL(umd_load_blob);
  76
  77 /**
  78  * umd_unload_blob - Disassociate @info from a previously loaded blob
  79  * @info: information about usermode driver
  80  *
  81  */
  82 int umd_unload_blob(struct umd_info *info)
  83 {
  84         if (WARN_ON_ONCE(!info->wd.mnt ||
  85                          !info->wd.dentry ||
  86                          info->wd.mnt->mnt_root != info->wd.dentry))
  87                 return -EINVAL;
  88
  89         kern_unmount(info->wd.mnt);
  90         info->wd.mnt = NULL;
  91         info->wd.dentry = NULL;
  92         return 0;
  93 }
  94 EXPORT_SYMBOL_GPL(umd_unload_blob);
  95
  96 static int umd_setup(struct subprocess_info *info, struct cred *new)
  97 {
  98         struct umd_info *umd_info = info->data;
  99         struct file *from_umh[2];
 100         struct file *to_umh[2];
 101         int err;
 102
 103         /* create pipe to send data to umh */
 104         err = create_pipe_files(to_umh, 0);
 105         if (err)
 106                 return err;
 107         err = replace_fd(0, to_umh[0], 0);
 108         fput(to_umh[0]);
 109         if (err < 0) {
 110                 fput(to_umh[1]);
 111                 return err;
 112         }
 113
 114         /* create pipe to receive data from umh */
 115         err = create_pipe_files(from_umh, 0);
 116         if (err) {
 117                 fput(to_umh[1]);
 118                 replace_fd(0, NULL, 0);
 119                 return err;
 120         }
 121         err = replace_fd(1, from_umh[1], 0);
 122         fput(from_umh[1]);
 123         if (err < 0) {
 124                 fput(to_umh[1]);
 125                 replace_fd(0, NULL, 0);
 126                 fput(from_umh[0]);
 127                 return err;
 128         }
 129
 130         set_fs_pwd(current->fs, &umd_info->wd);
 131         umd_info->pipe_to_umh = to_umh[1];
 132         umd_info->pipe_from_umh = from_umh[0];
 133         umd_info->tgid = get_pid(task_tgid(current));
 134         return 0;
 135 }
 136
 137 static void umd_cleanup(struct subprocess_info *info)
 138 {
 139         struct umd_info *umd_info = info->data;
 140
 141         /* cleanup if umh_setup() was successful but exec failed */
 142         if (info->retval)
 143                 umd_cleanup_helper(umd_info);
 144 }
 145
 146 /**
 147  * umd_cleanup_helper - release the resources which were allocated in umd_setup
 148  * @info: information about usermode driver
 149  */
 150 void umd_cleanup_helper(struct umd_info *info)
 151 {
 152         fput(info->pipe_to_umh);
 153         fput(info->pipe_from_umh);
 154         put_pid(info->tgid);
 155         info->tgid = NULL;
 156 }
 157 EXPORT_SYMBOL_GPL(umd_cleanup_helper);
 158
 159 /**
 160  * fork_usermode_driver - fork a usermode driver
 161  * @info: information about usermode driver (shouldn't be NULL)
 162  *
 163  * Returns either negative error or zero which indicates success in
 164  * executing a usermode driver. In such case 'struct umd_info *info'
 165  * is populated with two pipes and a tgid of the process. The caller is
 166  * responsible for health check of the user process, killing it via
 167  * tgid, and closing the pipes when user process is no longer needed.
 168  */
 169 int fork_usermode_driver(struct umd_info *info)
 170 {
 171         struct subprocess_info *sub_info;
 172         const char *argv[] = { info->driver_name, NULL };
 173         int err;
 174
 175         if (WARN_ON_ONCE(info->tgid))
 176                 return -EBUSY;
 177
 178         err = -ENOMEM;
 179         sub_info = call_usermodehelper_setup(info->driver_name,
 180                                              (char **)argv, NULL, GFP_KERNEL,
 181                                              umd_setup, umd_cleanup, info);
 182         if (!sub_info)
 183                 goto out;
 184
 185         err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 186 out:
 187         return err;
 188 }
 189 EXPORT_SYMBOL_GPL(fork_usermode_driver);
 190
 191