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![Kees Cook](/assets/img/avatar_default.png)
To perform partial reads, callers of kernel_read_file*() must have a non-NULL file_size argument and a preallocated buffer. The new "offset" argument can then be used to seek to specific locations in the file to fill the buffer to, at most, "buf_size" per call. Where possible, the LSM hooks can report whether a full file has been read or not so that the contents can be reasoned about. Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20201002173828.2099543-14-keescook@chromium.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
189 lines
4.4 KiB
C
189 lines
4.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/fs.h>
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#include <linux/fs_struct.h>
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#include <linux/kernel_read_file.h>
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#include <linux/security.h>
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#include <linux/vmalloc.h>
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/**
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* kernel_read_file() - read file contents into a kernel buffer
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*
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* @file file to read from
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* @offset where to start reading from (see below).
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* @buf pointer to a "void *" buffer for reading into (if
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* *@buf is NULL, a buffer will be allocated, and
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* @buf_size will be ignored)
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* @buf_size size of buf, if already allocated. If @buf not
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* allocated, this is the largest size to allocate.
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* @file_size if non-NULL, the full size of @file will be
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* written here.
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* @id the kernel_read_file_id identifying the type of
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* file contents being read (for LSMs to examine)
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*
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* @offset must be 0 unless both @buf and @file_size are non-NULL
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* (i.e. the caller must be expecting to read partial file contents
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* via an already-allocated @buf, in at most @buf_size chunks, and
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* will be able to determine when the entire file was read by
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* checking @file_size). This isn't a recommended way to read a
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* file, though, since it is possible that the contents might
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* change between calls to kernel_read_file().
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*
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* Returns number of bytes read (no single read will be bigger
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* than INT_MAX), or negative on error.
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*
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*/
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int kernel_read_file(struct file *file, loff_t offset, void **buf,
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size_t buf_size, size_t *file_size,
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enum kernel_read_file_id id)
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{
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loff_t i_size, pos;
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size_t copied;
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void *allocated = NULL;
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bool whole_file;
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int ret;
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if (offset != 0 && (!*buf || !file_size))
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return -EINVAL;
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if (!S_ISREG(file_inode(file)->i_mode))
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return -EINVAL;
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ret = deny_write_access(file);
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if (ret)
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return ret;
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i_size = i_size_read(file_inode(file));
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if (i_size <= 0) {
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ret = -EINVAL;
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goto out;
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}
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/* The file is too big for sane activities. */
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if (i_size > INT_MAX) {
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ret = -EFBIG;
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goto out;
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}
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/* The entire file cannot be read in one buffer. */
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if (!file_size && offset == 0 && i_size > buf_size) {
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ret = -EFBIG;
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goto out;
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}
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whole_file = (offset == 0 && i_size <= buf_size);
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ret = security_kernel_read_file(file, id, whole_file);
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if (ret)
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goto out;
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if (file_size)
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*file_size = i_size;
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if (!*buf)
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*buf = allocated = vmalloc(i_size);
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if (!*buf) {
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ret = -ENOMEM;
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goto out;
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}
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pos = offset;
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copied = 0;
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while (copied < buf_size) {
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ssize_t bytes;
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size_t wanted = min_t(size_t, buf_size - copied,
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i_size - pos);
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bytes = kernel_read(file, *buf + copied, wanted, &pos);
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if (bytes < 0) {
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ret = bytes;
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goto out_free;
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}
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if (bytes == 0)
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break;
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copied += bytes;
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}
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if (whole_file) {
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if (pos != i_size) {
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ret = -EIO;
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goto out_free;
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}
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ret = security_kernel_post_read_file(file, *buf, i_size, id);
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}
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out_free:
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if (ret < 0) {
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if (allocated) {
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vfree(*buf);
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*buf = NULL;
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}
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}
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out:
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allow_write_access(file);
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return ret == 0 ? copied : ret;
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}
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EXPORT_SYMBOL_GPL(kernel_read_file);
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int kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
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size_t buf_size, size_t *file_size,
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enum kernel_read_file_id id)
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{
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struct file *file;
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int ret;
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if (!path || !*path)
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return -EINVAL;
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file = filp_open(path, O_RDONLY, 0);
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if (IS_ERR(file))
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return PTR_ERR(file);
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ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
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fput(file);
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return ret;
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}
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EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
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int kernel_read_file_from_path_initns(const char *path, loff_t offset,
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void **buf, size_t buf_size,
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size_t *file_size,
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enum kernel_read_file_id id)
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{
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struct file *file;
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struct path root;
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int ret;
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if (!path || !*path)
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return -EINVAL;
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task_lock(&init_task);
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get_fs_root(init_task.fs, &root);
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task_unlock(&init_task);
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file = file_open_root(root.dentry, root.mnt, path, O_RDONLY, 0);
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path_put(&root);
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if (IS_ERR(file))
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return PTR_ERR(file);
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ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
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fput(file);
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return ret;
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}
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EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
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int kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
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size_t buf_size, size_t *file_size,
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enum kernel_read_file_id id)
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{
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struct fd f = fdget(fd);
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int ret = -EBADF;
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if (!f.file)
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goto out;
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ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id);
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out:
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fdput(f);
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return ret;
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}
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EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);
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