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180 lines · 4.2 KiB

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 ssize_t ret;
154
155 if (!path || !*path)
156 return -EINVAL;
157
158 scoped_with_init_fs()
159 file = filp_open(path, O_RDONLY, 0);
160 if (IS_ERR(file))
161 return PTR_ERR(file);
162
163 ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
164 fput(file);
165 return ret;
166}
167EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
168
169ssize_t kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
170 size_t buf_size, size_t *file_size,
171 enum kernel_read_file_id id)
172{
173 CLASS(fd, f)(fd);
174
175 if (fd_empty(f) || !(fd_file(f)->f_mode & FMODE_READ))
176 return -EBADF;
177
178 return kernel_read_file(fd_file(f), offset, buf, buf_size, file_size, id);
179}
180EXPORT_SYMBOL_GPL(kernel_read_file_from_fd);