1// Copyright (C) 2015 Konstantin Ritt <ritt.ks@gmail.com>
2// Copyright (C) 2016 The Qt Company Ltd.
3// Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Tobias Koenig <tobias.koenig@kdab.com>
4// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
5// Qt-Security score:significant reason:default
6
7#include "qsharedmemory.h"
8#include "qsharedmemory_p.h"
9#include "qtipccommon_p.h"
10#include <qfile.h>
11
12#include <errno.h>
13
14#if QT_CONFIG(sharedmemory)
15#if QT_CONFIG(posix_shm)
16#include <sys/types.h>
17#include <sys/mman.h>
18#include <sys/stat.h>
19#include <fcntl.h>
20#include <unistd.h>
21
22#include "private/qcore_unix_p.h"
23
24#ifndef O_CLOEXEC
25# define O_CLOEXEC 0
26#endif
27
28QT_BEGIN_NAMESPACE
29
30using namespace Qt::StringLiterals;
31using namespace QtIpcCommon;
32
33bool QSharedMemoryPosix::runtimeSupportCheck()
34{
35 static const bool result = []() {
36 (void)shm_open(name: "", oflag: 0, mode: 0); // this WILL fail
37 return errno != ENOSYS;
38 }();
39 return result;
40}
41
42bool QSharedMemoryPosix::handle(QSharedMemoryPrivate *self)
43{
44 // don't allow making handles on empty keys
45 if (self->nativeKey.isEmpty()) {
46 self->setError(e: QSharedMemory::KeyError,
47 message: QSharedMemory::tr(s: "%1: key is empty").arg(a: "QSharedMemory::handle"_L1));
48 return false;
49 }
50
51 return true;
52}
53
54bool QSharedMemoryPosix::cleanHandle(QSharedMemoryPrivate *)
55{
56 if (hand != -1)
57 qt_safe_close(fd: hand);
58 hand = -1;
59
60 return true;
61}
62
63bool QSharedMemoryPosix::create(QSharedMemoryPrivate *self, qsizetype size)
64{
65 if (!handle(self))
66 return false;
67
68 const QByteArray shmName = QFile::encodeName(fileName: self->nativeKey.nativeKey());
69
70 int fd;
71 QT_EINTR_LOOP(fd, ::shm_open(shmName.constData(), O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0600));
72 if (fd == -1) {
73 const int errorNumber = errno;
74 const auto function = "QSharedMemory::attach (shm_open)"_L1;
75 switch (errorNumber) {
76 case EINVAL:
77 self->setError(e: QSharedMemory::KeyError,
78 message: QSharedMemory::tr(s: "%1: bad name").arg(a: function));
79 break;
80 default:
81 self->setUnixErrorString(function);
82 }
83 return false;
84 }
85
86 // the size may only be set once
87 int ret;
88 QT_EINTR_LOOP(ret, QT_FTRUNCATE(fd, size));
89 if (ret == -1) {
90 self->setUnixErrorString("QSharedMemory::create (ftruncate)"_L1);
91 qt_safe_close(fd);
92 return false;
93 }
94
95 qt_safe_close(fd);
96
97 return true;
98}
99
100bool QSharedMemoryPosix::attach(QSharedMemoryPrivate *self, QSharedMemory::AccessMode mode)
101{
102 const QByteArray shmName = QFile::encodeName(fileName: self->nativeKey.nativeKey());
103
104 const int oflag = (mode == QSharedMemory::ReadOnly ? O_RDONLY : O_RDWR);
105 const mode_t omode = (mode == QSharedMemory::ReadOnly ? 0400 : 0600);
106
107 QT_EINTR_LOOP(hand, ::shm_open(shmName.constData(), oflag | O_CLOEXEC, omode));
108 if (hand == -1) {
109 const int errorNumber = errno;
110 const auto function = "QSharedMemory::attach (shm_open)"_L1;
111 switch (errorNumber) {
112 case EINVAL:
113 self->setError(e: QSharedMemory::KeyError,
114 message: QSharedMemory::tr(s: "%1: bad name").arg(a: function));
115 break;
116 default:
117 self->setUnixErrorString(function);
118 }
119 hand = -1;
120 return false;
121 }
122
123 // grab the size
124 QT_STATBUF st;
125 if (QT_FSTAT(fd: hand, buf: &st) == -1) {
126 self->setUnixErrorString("QSharedMemory::attach (fstat)"_L1);
127 cleanHandle(self);
128 return false;
129 }
130 self->size = qsizetype(st.st_size);
131
132 // grab the memory
133 const int mprot = (mode == QSharedMemory::ReadOnly ? PROT_READ : PROT_READ | PROT_WRITE);
134 self->memory = QT_MMAP(addr: 0, len: size_t(self->size), prot: mprot, MAP_SHARED, fd: hand, offset: 0);
135 if (self->memory == MAP_FAILED || !self->memory) {
136 self->setUnixErrorString("QSharedMemory::attach (mmap)"_L1);
137 cleanHandle(self);
138 self->memory = 0;
139 self->size = 0;
140 return false;
141 }
142
143#ifdef F_ADD_SEALS
144 // Make sure the shared memory region will not shrink
145 // otherwise someone could cause SIGBUS on us.
146 // (see http://lwn.net/Articles/594919/)
147 fcntl(fd: hand, F_ADD_SEALS, F_SEAL_SHRINK);
148#endif
149
150 return true;
151}
152
153bool QSharedMemoryPosix::detach(QSharedMemoryPrivate *self)
154{
155 // detach from the memory segment
156 if (::munmap(addr: self->memory, len: size_t(self->size)) == -1) {
157 self->setUnixErrorString("QSharedMemory::detach (munmap)"_L1);
158 return false;
159 }
160 self->memory = 0;
161 self->size = 0;
162
163#ifdef Q_OS_QNX
164 // On QNX the st_nlink field of struct stat contains the number of
165 // active shm_open() connections to the shared memory file, so we
166 // can use it to automatically clean up the file once the last
167 // user has detached from it.
168
169 // get the number of current attachments
170 int shm_nattch = 0;
171 QT_STATBUF st;
172 if (QT_FSTAT(hand, &st) == 0) {
173 // subtract 2 from linkcount: one for our own open and one for the dir entry
174 shm_nattch = st.st_nlink - 2;
175 }
176
177 cleanHandle(self);
178
179 // if there are no attachments then unlink the shared memory
180 if (shm_nattch == 0) {
181 const QByteArray shmName = QFile::encodeName(self->nativeKey.nativeKey());
182 if (::shm_unlink(shmName.constData()) == -1 && errno != ENOENT)
183 self->setUnixErrorString("QSharedMemory::detach (shm_unlink)"_L1);
184 }
185#else
186 // On non-QNX systems (tested Linux and Haiku), the st_nlink field is always 1,
187 // so we'll simply leak the shared memory files.
188 cleanHandle(self);
189#endif
190
191 return true;
192}
193
194QT_END_NAMESPACE
195
196#endif // QT_CONFIG(posix_shm)
197#endif // QT_CONFIG(sharedmemory)
198

source code of qtbase/src/corelib/ipc/qsharedmemory_posix.cpp