1 // Copyright 2019 Google LLC
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "sandboxed_api/embed_file.h"
16
17 #include <fcntl.h>
18 #include <sys/stat.h>
19 #include <unistd.h>
20
21 #include <string>
22
23 #include "sandboxed_api/file_toc.h"
24 #include "absl/strings/str_cat.h"
25 #include "absl/synchronization/mutex.h"
26 #include "sandboxed_api/sandbox2/util.h"
27 #include "sandboxed_api/util/fileops.h"
28 #include "sandboxed_api/util/raw_logging.h"
29
30 namespace sapi {
31
32 namespace {
33
34 #ifndef F_ADD_SEALS
35 #define F_ADD_SEALS 1033
36 #define F_SEAL_SEAL 0x0001
37 #define F_SEAL_SHRINK 0x0002
38 #define F_SEAL_GROW 0x0004
39 #define F_SEAL_WRITE 0x0008
40 #endif
41
SealFile(int fd)42 bool SealFile(int fd) {
43 constexpr int kMaxRetries = 10;
44 for (int i = 0; i < kMaxRetries; ++i) {
45 if (fcntl(fd, F_ADD_SEALS,
46 F_SEAL_SEAL | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE) == 0) {
47 return true;
48 }
49 }
50 return false;
51 }
52
53 } // namespace
54
instance()55 EmbedFile* EmbedFile::instance() {
56 static auto* embed_file_instance = new EmbedFile();
57 return embed_file_instance;
58 }
59
CreateFdForFileToc(const FileToc * toc)60 int EmbedFile::CreateFdForFileToc(const FileToc* toc) {
61 // Create a memfd/temp file and write contents of the SAPI library to it.
62 int fd = -1;
63 if (!sandbox2::util::CreateMemFd(&fd, toc->name)) {
64 SAPI_RAW_LOG(ERROR, "Couldn't create a temporary file for TOC name '%s'",
65 toc->name);
66 return -1;
67 }
68 file_util::fileops::FDCloser embed_fd(fd);
69
70 if (!file_util::fileops::WriteToFD(embed_fd.get(), toc->data, toc->size)) {
71 SAPI_RAW_PLOG(ERROR, "Couldn't write SAPI embed file '%s' to memfd file",
72 toc->name);
73 return -1;
74 }
75
76 // Make the underlying file non-writeable.
77 if (fchmod(embed_fd.get(),
78 S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH) == -1) {
79 SAPI_RAW_PLOG(ERROR, "Could't make FD=%d RX-only", embed_fd.get());
80 return -1;
81 }
82
83 // Seal the file
84 if (!SealFile(embed_fd.get())) {
85 SAPI_RAW_PLOG(ERROR, "Couldn't apply file seals to FD=%d", embed_fd.get());
86 return -1;
87 }
88
89 // Instead of working around problems with CRIU we reopen the file as
90 // read-only.
91 fd = open(absl::StrCat("/proc/", getpid(), "/fd/", embed_fd.get()).c_str(),
92 O_RDONLY | O_CLOEXEC);
93 if (fd == -1) {
94 SAPI_RAW_PLOG(ERROR, "Couldn't reopen '%d' read-only through /proc",
95 embed_fd.get());
96 return -1;
97 }
98 return fd;
99 }
100
GetFdForFileToc(const FileToc * toc)101 int EmbedFile::GetFdForFileToc(const FileToc* toc) {
102 // Access to file_tocs_ must be guarded.
103 absl::MutexLock lock{&file_tocs_mutex_};
104
105 // If a file-descriptor for this toc already exists, just return it.
106 auto entry = file_tocs_.find(toc);
107 if (entry != file_tocs_.end()) {
108 SAPI_RAW_VLOG(3,
109 "Returning pre-existing embed file entry for '%s', fd: %d "
110 "(orig name: '%s')",
111 toc->name, entry->second, entry->first->name);
112 return entry->second;
113 }
114
115 int embed_fd = CreateFdForFileToc(toc);
116 if (embed_fd == -1) {
117 SAPI_RAW_LOG(ERROR, "Cannot create a file for FileTOC: '%s'", toc->name);
118 return -1;
119 }
120
121 SAPI_RAW_VLOG(1, "Created new embed file entry for '%s' with fd: %d",
122 toc->name, embed_fd);
123
124 file_tocs_[toc] = embed_fd;
125 return embed_fd;
126 }
127
GetDupFdForFileToc(const FileToc * toc)128 int EmbedFile::GetDupFdForFileToc(const FileToc* toc) {
129 int fd = GetFdForFileToc(toc);
130 if (fd == -1) {
131 return -1;
132 }
133 fd = dup(fd);
134 if (fd == -1) {
135 SAPI_RAW_PLOG(ERROR, "dup failed");
136 }
137 return fd;
138 }
139
140 } // namespace sapi
141