fs/kernel_read_file.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/fs.h>
   3 #include <linux/fs_struct.h>
   4 #include <linux/kernel_read_file.h>
   5 #include <linux/security.h>
   6 #include <linux/vmalloc.h>
   7
   8 /**
   9  * kernel_read_file() - read file contents into a kernel buffer
  10  *
  11  * @file        file to read from
  12  * @offset      where to start reading from (see below).
  13  * @buf         pointer to a "void *" buffer for reading into (if
  14  *              *@buf is NULL, a buffer will be allocated, and
  15  *              @buf_size will be ignored)
  16  * @buf_size    size of buf, if already allocated. If @buf not
  17  *              allocated, this is the largest size to allocate.
  18  * @file_size   if non-NULL, the full size of @file will be
  19  *              written here.
  20  * @id          the kernel_read_file_id identifying the type of
  21  *              file contents being read (for LSMs to examine)
  22  *
  23  * @offset must be 0 unless both @buf and @file_size are non-NULL
  24  * (i.e. the caller must be expecting to read partial file contents
  25  * via an already-allocated @buf, in at most @buf_size chunks, and
  26  * will be able to determine when the entire file was read by
  27  * checking @file_size). This isn't a recommended way to read a
  28  * file, though, since it is possible that the contents might
  29  * change between calls to kernel_read_file().
  30  *
  31  * Returns number of bytes read (no single read will be bigger
  32  * than INT_MAX), or negative on error.
  33  *
  34  */
  35 int kernel_read_file(struct file *file, loff_t offset, void **buf,
  36                      size_t buf_size, size_t *file_size,
  37                      enum kernel_read_file_id id)
  38 {
  39         loff_t i_size, pos;
  40         size_t copied;
  41         void *allocated = NULL;
  42         bool whole_file;
  43         int ret;
  44
  45         if (offset != 0 && (!*buf || !file_size))
  46                 return -EINVAL;
  47
  48         if (!S_ISREG(file_inode(file)->i_mode))
  49                 return -EINVAL;
  50
  51         ret = deny_write_access(file);
  52         if (ret)
  53                 return ret;
  54
  55         i_size = i_size_read(file_inode(file));
  56         if (i_size <= 0) {
  57                 ret = -EINVAL;
  58                 goto out;
  59         }
  60         /* The file is too big for sane activities. */
  61         if (i_size > INT_MAX) {
  62                 ret = -EFBIG;
  63                 goto out;
  64         }
  65         /* The entire file cannot be read in one buffer. */
  66         if (!file_size && offset == 0 && i_size > buf_size) {
  67                 ret = -EFBIG;
  68                 goto out;
  69         }
  70
  71         whole_file = (offset == 0 && i_size <= buf_size);
  72         ret = security_kernel_read_file(file, id, whole_file);
  73         if (ret)
  74                 goto out;
  75
  76         if (file_size)
  77                 *file_size = i_size;
  78
  79         if (!*buf)
  80                 *buf = allocated = vmalloc(i_size);
  81         if (!*buf) {
  82                 ret = -ENOMEM;
  83                 goto out;
  84         }
  85
  86         pos = offset;
  87         copied = 0;
  88         while (copied < buf_size) {
  89                 ssize_t bytes;
  90                 size_t wanted = min_t(size_t, buf_size - copied,
  91                                               i_size - pos);
  92
  93                 bytes = kernel_read(file, *buf + copied, wanted, &pos);
  94                 if (bytes < 0) {
  95                         ret = bytes;
  96                         goto out_free;
  97                 }
  98
  99                 if (bytes == 0)
 100                         break;
 101                 copied += bytes;
 102         }
 103
 104         if (whole_file) {
 105                 if (pos != i_size) {
 106                         ret = -EIO;
 107                         goto out_free;
 108                 }
 109
 110                 ret = security_kernel_post_read_file(file, *buf, i_size, id);
 111         }
 112
 113 out_free:
 114         if (ret < 0) {
 115                 if (allocated) {
 116                         vfree(*buf);
 117                         *buf = NULL;
 118                 }
 119         }
 120
 121 out:
 122         allow_write_access(file);
 123         return ret == 0 ? copied : ret;
 124 }
 125 EXPORT_SYMBOL_GPL(kernel_read_file);
 126
 127 int kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
 128                                size_t buf_size, size_t *file_size,
 129                                enum kernel_read_file_id id)
 130 {
 131         struct file *file;
 132         int ret;
 133
 134         if (!path || !*path)
 135                 return -EINVAL;
 136
 137         file = filp_open(path, O_RDONLY, 0);
 138         if (IS_ERR(file))
 139                 return PTR_ERR(file);
 140
 141         ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
 142         fput(file);
 143         return ret;
 144 }
 145 EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
 146
 147 int kernel_read_file_from_path_initns(const char *path, loff_t offset,
 148                                       void **buf, size_t buf_size,
 149                                       size_t *file_size,
 150                                       enum kernel_read_file_id id)
 151 {
 152         struct file *file;
 153         struct path root;
 154         int ret;
 155
 156         if (!path || !*path)
 157                 return -EINVAL;
 158
 159         task_lock(&init_task);
 160         get_fs_root(init_task.fs, &root);
 161         task_unlock(&init_task);
 162
 163         file = file_open_root(root.dentry, root.mnt, path, O_RDONLY, 0);
 164         path_put(&root);
 165         if (IS_ERR(file))
 166                 return PTR_ERR(file);
 167
 168         ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
 169         fput(file);
 170         return ret;
 171 }
 172 EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
 173
 174 int kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
 175                              size_t buf_size, size_t *file_size,
 176                              enum kernel_read_file_id id)
 177 {
 178         struct fd f = fdget(fd);
 179         int ret = -EBADF;
 180
 181         if (!f.file)
 182                 goto out;
 183
 184         ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id);
 185 out:
 186         fdput(f);
 187         return ret;
 188 }
 189 EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);