1 // Copyright 2013 The Flutter Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 // It is __imperative__ that the functions in this file are __not__ included in
6 // release or profile builds.
7 //
8 // They call into the "private" ptrace() API to ensure that the current process
9 // is being ptrace()-d. Only debug builds rely on ptrace(), and the ptrace() API
10 // is not allowed for use in the App Store, so we must exclude it from profile-
11 // and release-builds.
12 //
13 // When an app is launched from a host workstation (e.g. via Xcode or
14 // "ios-deploy"), the process is already ptrace()-d by debugserver. However,
15 // when an app is launched from the home screen, it is not, so for debug builds
16 // we initialize the ptrace() relationship via PT_TRACE_ME if necessary.
17 //
18 // Please see the following documents for more details:
19 // - go/decommissioning-dbc
20 // - go/decommissioning-dbc-engine
21 // - go/decommissioning-dbc-tools
22 #include "flutter/common/settings.h"
23 #include "flutter/fml/build_config.h" // For OS_IOS.
24
25 #if OS_IOS && (FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG)
26
27 // These headers should only be needed in debug mode.
28 #include <sys/sysctl.h>
29 #include <sys/types.h>
30
31 #define PT_TRACE_ME 0
32 #define PT_SIGEXC 12
33 extern "C" int ptrace(int request, pid_t pid, caddr_t addr, int data);
34
DebuggedIOS(const flutter::Settings & vm_settings)35 static bool DebuggedIOS(const flutter::Settings& vm_settings) {
36 // Only the Flutter CLI passes "--enable-checked-mode". Therefore, if the flag
37 // is present, we have been launched by "ios-deploy" via "debugserver".
38 //
39 // We choose this flag because it is always passed to launch debug builds.
40 if (vm_settings.enable_checked_mode) {
41 return true;
42 }
43
44 // Use "sysctl()" to check if we're currently being debugged (e.g. by Xcode).
45 // We could also check "getppid() != 1" (launchd), but this is more direct.
46 const pid_t self = getpid();
47 int mib[5] = {CTL_KERN, KERN_PROC, KERN_PROC_PID, self, 0};
48
49 auto proc = std::make_unique<struct kinfo_proc>();
50 size_t proc_size = sizeof(struct kinfo_proc);
51 if (sysctl(mib, 4, proc.get(), &proc_size, nullptr, 0) < 0) {
52 FML_LOG(ERROR) << "Could not execute sysctl() to get current process info: "
53 << strerror(errno);
54 return false;
55 }
56
57 return proc->kp_proc.p_flag & P_TRACED;
58 }
59
EnsureDebuggedIOS(const flutter::Settings & vm_settings)60 void EnsureDebuggedIOS(const flutter::Settings& vm_settings) {
61 if (DebuggedIOS(vm_settings)) {
62 return;
63 }
64
65 if (ptrace(PT_TRACE_ME, 0, nullptr, 0) == -1) {
66 FML_LOG(ERROR) << "Could not call ptrace(PT_TRACE_ME): " << strerror(errno);
67 // No use trying PT_SIGEXC -- it's only needed if PT_TRACE_ME succeeds.
68 return;
69 }
70 if (ptrace(PT_SIGEXC, 0, nullptr, 0) == -1) {
71 FML_LOG(ERROR) << "Could not call ptrace(PT_SIGEXC): " << strerror(errno);
72 }
73
74 // The previous operation causes this process to not be reaped after it
75 // terminates (even if PT_SIGEXC fails). Issue a warning to the console every
76 // (approximiately) maxproc/10 leaks. See the links above for an explanation
77 // of this issue.
78 size_t maxproc = 0;
79 size_t maxproc_size = sizeof(size_t);
80 const int sysctl_result =
81 sysctlbyname("kern.maxproc", &maxproc, &maxproc_size, nullptr, 0);
82 if (sysctl_result < 0) {
83 FML_LOG(ERROR)
84 << "Could not execute sysctl() to determine process count limit: "
85 << strerror(errno);
86 }
87
88 const char* warning =
89 "Launching a debug-mode app from the home screen may cause problems.\n"
90 "Please compile a profile-/release-build, launch your app via \"flutter "
91 "run\", or see https://github.com/flutter/flutter/wiki/"
92 "PID-leak-in-iOS-debug-builds-launched-from-home-screen for details.";
93
94 if (vm_settings.verbose_logging // used for testing and also informative
95 || sysctl_result < 0 // could not determine maximum process count
96 || maxproc / 10 == 0 // avoid division (%) by 0
97 || getpid() % (maxproc / 10) == 0) // warning every ~maxproc/10 leaks
98 {
99 FML_LOG(ERROR) << warning;
100 }
101 }
102
103 #endif // OS_IOS && (FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG)
104