1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
|
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// base::AddressIsReadable() probes an address to see whether it is readable,
// without faulting.
#include "absl/debugging/internal/address_is_readable.h"
#if !defined(__linux__) || defined(__ANDROID__)
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace debugging_internal {
// On platforms other than Linux, just return true.
bool AddressIsReadable(const void* /* addr */) { return true; }
} // namespace debugging_internal
ABSL_NAMESPACE_END
} // namespace absl
#else
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <cerrno>
#include "absl/base/internal/errno_saver.h"
#include "absl/base/internal/raw_logging.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace debugging_internal {
bool AddressIsReadable(const void *addr) {
int fd = 0;
absl::base_internal::ErrnoSaver errno_saver;
for (int j = 0; j < 2; j++) {
// Here we probe with some syscall which
// - accepts a one-byte region of user memory as input
// - tests for EFAULT before other validation
// - has no problematic side-effects
//
// connect(2) works for this. It copies the address into kernel
// memory before any validation beyond requiring an open fd.
// But a one byte address is never valid (sa_family is two bytes),
// so the call cannot succeed and change any state.
//
// This strategy depends on Linux implementation details,
// so we rely on the test to alert us if it stops working.
//
// Some discarded past approaches:
// - msync() doesn't reject PROT_NONE regions
// - write() on /dev/null doesn't return EFAULT
// - write() on a pipe requires creating it and draining the writes
//
// Use syscall(SYS_connect, ...) instead of connect() to prevent ASAN
// and other checkers from complaining about accesses to arbitrary memory.
do {
ABSL_RAW_CHECK(syscall(SYS_connect, fd, addr, 1) == -1,
"should never succeed");
} while (errno == EINTR);
if (errno == EFAULT) return false;
if (errno == EBADF) {
if (j != 0) {
// Unclear what happened.
ABSL_RAW_LOG(ERROR, "unexpected EBADF on fd %d", fd);
return false;
}
// fd 0 must have been closed. Try opening it again.
// Note: we shouldn't leak too many file descriptors here, since we expect
// to get fd==0 reopened.
fd = open("/dev/null", O_RDONLY);
if (fd == -1) {
ABSL_RAW_LOG(ERROR, "can't open /dev/null");
return false;
}
} else {
// probably EINVAL or ENOTSOCK; we got past EFAULT validation.
return true;
}
}
ABSL_RAW_CHECK(false, "unreachable");
return false;
}
} // namespace debugging_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif
|
