1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Ioctl to read verity metadata
4 *
5 * Copyright 2021 Google LLC
6 */
7
8 #include "fsverity_private.h"
9
10 #include <linux/backing-dev.h>
11 #include <linux/highmem.h>
12 #include <linux/sched/signal.h>
13 #include <linux/uaccess.h>
14
15 static int fsverity_read_merkle_tree(struct inode *inode,
16 const struct fsverity_info *vi,
17 void __user *buf, u64 offset, int length)
18 {
19 const struct fsverity_operations *vops = inode->i_sb->s_vop;
20 u64 end_offset;
21 unsigned int offs_in_page;
22 pgoff_t index, last_index;
23 int retval = 0;
24 int err = 0;
25
26 end_offset = min(offset + length, vi->tree_params.tree_size);
27 if (offset >= end_offset)
28 return 0;
29 offs_in_page = offset_in_page(offset);
30 last_index = (end_offset - 1) >> PAGE_SHIFT;
31
32 /*
33 * Iterate through each Merkle tree page in the requested range and copy
34 * the requested portion to userspace. Note that the Merkle tree block
35 * size isn't important here, as we are returning a byte stream; i.e.,
36 * we can just work with pages even if the tree block size != PAGE_SIZE.
37 */
38 for (index = offset >> PAGE_SHIFT; index <= last_index; index++) {
39 unsigned long num_ra_pages =
40 min_t(unsigned long, last_index - index + 1,
41 inode->i_sb->s_bdi->io_pages);
42 unsigned int bytes_to_copy = min_t(u64, end_offset - offset,
43 PAGE_SIZE - offs_in_page);
44 struct page *page;
45 const void *virt;
46
47 page = vops->read_merkle_tree_page(inode, index, num_ra_pages);
48 if (IS_ERR(page)) {
49 err = PTR_ERR(page);
50 fsverity_err(inode,
51 "Error %d reading Merkle tree page %lu",
52 err, index);
53 break;
54 }
55
56 virt = kmap_local_page(page);
57 if (copy_to_user(buf, virt + offs_in_page, bytes_to_copy)) {
58 kunmap_local(virt);
59 put_page(page);
60 err = -EFAULT;
61 break;
62 }
63 kunmap_local(virt);
64 put_page(page);
65
66 retval += bytes_to_copy;
67 buf += bytes_to_copy;
68 offset += bytes_to_copy;
69
70 if (fatal_signal_pending(current)) {
71 err = -EINTR;
72 break;
73 }
74 cond_resched();
75 offs_in_page = 0;
76 }
77 return retval ? retval : err;
78 }
79
80 /* Copy the requested portion of the buffer to userspace. */
81 static int fsverity_read_buffer(void __user *dst, u64 offset, int length,
82 const void *src, size_t src_length)
83 {
84 if (offset >= src_length)
85 return 0;
86 src += offset;
87 src_length -= offset;
88
89 length = min_t(size_t, length, src_length);
90
91 if (copy_to_user(dst, src, length))
92 return -EFAULT;
93
94 return length;
95 }
96
97 static int fsverity_read_descriptor(struct inode *inode,
98 void __user *buf, u64 offset, int length)
99 {
100 struct fsverity_descriptor *desc;
101 size_t desc_size;
102 int res;
103
104 res = fsverity_get_descriptor(inode, &desc);
105 if (res)
106 return res;
107
108 /* don't include the builtin signature */
109 desc_size = offsetof(struct fsverity_descriptor, signature);
110 desc->sig_size = 0;
111
112 res = fsverity_read_buffer(buf, offset, length, desc, desc_size);
113
114 kfree(desc);
115 return res;
116 }
117
118 static int fsverity_read_signature(struct inode *inode,
119 void __user *buf, u64 offset, int length)
120 {
121 struct fsverity_descriptor *desc;
122 int res;
123
124 res = fsverity_get_descriptor(inode, &desc);
125 if (res)
126 return res;
127
128 if (desc->sig_size == 0) {
129 res = -ENODATA;
130 goto out;
131 }
132
133 /*
134 * Include only the builtin signature. fsverity_get_descriptor()
135 * already verified that sig_size is in-bounds.
136 */
137 res = fsverity_read_buffer(buf, offset, length, desc->signature,
138 le32_to_cpu(desc->sig_size));
139 out:
140 kfree(desc);
141 return res;
142 }
143
144 /**
145 * fsverity_ioctl_read_metadata() - read verity metadata from a file
146 * @filp: file to read the metadata from
147 * @uarg: user pointer to fsverity_read_metadata_arg
148 *
149 * Return: length read on success, 0 on EOF, -errno on failure
150 */
151 int fsverity_ioctl_read_metadata(struct file *filp, const void __user *uarg)
152 {
153 struct inode *inode = file_inode(filp);
154 const struct fsverity_info *vi;
155 struct fsverity_read_metadata_arg arg;
156 int length;
157 void __user *buf;
158
159 vi = fsverity_get_info(inode);
160 if (!vi)
161 return -ENODATA; /* not a verity file */
162 /*
163 * Note that we don't have to explicitly check that the file is open for
164 * reading, since verity files can only be opened for reading.
165 */
166
167 if (copy_from_user(&arg, uarg, sizeof(arg)))
168 return -EFAULT;
169
170 if (arg.__reserved)
171 return -EINVAL;
172
173 /* offset + length must not overflow. */
174 if (arg.offset + arg.length < arg.offset)
175 return -EINVAL;
176
177 /* Ensure that the return value will fit in INT_MAX. */
178 length = min_t(u64, arg.length, INT_MAX);
179
180 buf = u64_to_user_ptr(arg.buf_ptr);
181
182 switch (arg.metadata_type) {
183 case FS_VERITY_METADATA_TYPE_MERKLE_TREE:
184 return fsverity_read_merkle_tree(inode, vi, buf, arg.offset,
185 length);
186 case FS_VERITY_METADATA_TYPE_DESCRIPTOR:
187 return fsverity_read_descriptor(inode, buf, arg.offset, length);
188 case FS_VERITY_METADATA_TYPE_SIGNATURE:
189 return fsverity_read_signature(inode, buf, arg.offset, length);
190 default:
191 return -EINVAL;
192 }
193 }
194 EXPORT_SYMBOL_GPL(fsverity_ioctl_read_metadata);
195
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