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 SSIZE_MAX), or negative on error.
 33 *
 34 */
 35ssize_t 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	ssize_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 > SSIZE_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
113out_free:
114	if (ret < 0) {
115		if (allocated) {
116			vfree(*buf);
117			*buf = NULL;
118		}
119	}
120
121out:
122	allow_write_access(file);
123	return ret == 0 ? copied : ret;
124}
125EXPORT_SYMBOL_GPL(kernel_read_file);
126
127ssize_t 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	ssize_t 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}
145EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
146
147ssize_t 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	ssize_t 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, 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}
172EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
173
174ssize_t 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	CLASS(fd, f)(fd);
179
180	if (fd_empty(f) || !(fd_file(f)->f_mode & FMODE_READ))
181		return -EBADF;
182
183	return kernel_read_file(fd_file(f), offset, buf, buf_size, file_size, id);
184}
185EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);