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Merge \"debuggerd: verify that traced threads belong to the right process.\" into nyc-dev

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am: d3d04f4d72

Change-Id: Ibe7073dfbb8f35acaf494fca82ac6a855a34c704
This commit is contained in:
Josh Gao 2016-07-19 20:34:17 +00:00 committed by android-build-merger
commit 1a0d789268
1 changed files with 63 additions and 13 deletions
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76
debuggerd/debuggerd.cpp
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@ -183,6 +183,16 @@ out:
return allowed;
}
static bool pid_contains_tid(pid_t pid, pid_t tid) {
char task_path[PATH_MAX];
if (snprintf(task_path, PATH_MAX, "/proc/%d/task/%d", pid, tid) >= PATH_MAX) {
ALOGE("debuggerd: task path overflow (pid = %d, tid = %d)\n", pid, tid);
exit(1);
}
return access(task_path, F_OK) == 0;
}
static int read_request(int fd, debugger_request_t* out_request) {
ucred cr;
socklen_t len = sizeof(cr);
@ -227,16 +237,13 @@ static int read_request(int fd, debugger_request_t* out_request) {
if (msg.action == DEBUGGER_ACTION_CRASH) {
// Ensure that the tid reported by the crashing process is valid.
char buf[64];
struct stat s;
snprintf(buf, sizeof buf, "/proc/%d/task/%d", out_request->pid, out_request->tid);
if (stat(buf, &s)) {
ALOGE("tid %d does not exist in pid %d. ignoring debug request\n",
out_request->tid, out_request->pid);
// This check needs to happen again after ptracing the requested thread to prevent a race.
if (!pid_contains_tid(out_request->pid, out_request->tid)) {
ALOGE("tid %d does not exist in pid %d. ignoring debug request\n", out_request->tid,
out_request->pid);
return -1;
}
} else if (cr.uid == 0
|| (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
} else if (cr.uid == 0 || (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
// Only root or system can ask us to attach to any process and dump it explicitly.
// However, system is only allowed to collect backtraces but cannot dump tombstones.
status = get_process_info(out_request->tid, &out_request->pid,
@ -413,10 +420,31 @@ static void redirect_to_32(int fd, debugger_request_t* request) {
}
#endif
static void ptrace_siblings(pid_t pid, pid_t main_tid, std::set<pid_t>& tids) {
char task_path[64];
// Attach to a thread, and verify that it's still a member of the given process
static bool ptrace_attach_thread(pid_t pid, pid_t tid) {
if (ptrace(PTRACE_ATTACH, tid, 0, 0) != 0) {
return false;
}
snprintf(task_path, sizeof(task_path), "/proc/%d/task", pid);
// Make sure that the task we attached to is actually part of the pid we're dumping.
if (!pid_contains_tid(pid, tid)) {
if (ptrace(PTRACE_DETACH, tid, 0, 0) != 0) {
ALOGE("debuggerd: failed to detach from thread '%d'", tid);
exit(1);
}
return false;
}
return true;
}
static void ptrace_siblings(pid_t pid, pid_t main_tid, std::set<pid_t>& tids) {
char task_path[PATH_MAX];
if (snprintf(task_path, PATH_MAX, "/proc/%d/task", pid) >= PATH_MAX) {
ALOGE("debuggerd: task path overflow (pid = %d)\n", pid);
abort();
}
std::unique_ptr<DIR, int (*)(DIR*)> d(opendir(task_path), closedir);
@ -443,7 +471,7 @@ static void ptrace_siblings(pid_t pid, pid_t main_tid, std::set<pid_t>& tids) {
continue;
}
if (ptrace(PTRACE_ATTACH, tid, 0, 0) < 0) {
if (!ptrace_attach_thread(pid, tid)) {
ALOGE("debuggerd: ptrace attach to %d failed: %s", tid, strerror(errno));
continue;
}
@ -568,11 +596,33 @@ static void worker_process(int fd, debugger_request_t& request) {
// debugger_signal_handler().
// Attach to the target process.
if (ptrace(PTRACE_ATTACH, request.tid, 0, 0) != 0) {
if (!ptrace_attach_thread(request.pid, request.tid)) {
ALOGE("debuggerd: ptrace attach failed: %s", strerror(errno));
exit(1);
}
// DEBUGGER_ACTION_CRASH requests can come from arbitrary processes and the tid field in the
// request is sent from the other side. If an attacker can cause a process to be spawned with the
// pid of their process, they could trick debuggerd into dumping that process by exiting after
// sending the request. Validate the trusted request.uid/gid to defend against this.
if (request.action == DEBUGGER_ACTION_CRASH) {
pid_t pid;
uid_t uid;
gid_t gid;
if (get_process_info(request.tid, &pid, &uid, &gid) != 0) {
ALOGE("debuggerd: failed to get process info for tid '%d'", request.tid);
exit(1);
}
if (pid != request.pid || uid != request.uid || gid != request.gid) {
ALOGE(
"debuggerd: attached task %d does not match request: "
"expected pid=%d,uid=%d,gid=%d, actual pid=%d,uid=%d,gid=%d",
request.tid, request.pid, request.uid, request.gid, pid, uid, gid);
exit(1);
}
}
// Don't attach to the sibling threads if we want to attach gdb.
// Supposedly, it makes the process less reliable.
bool attach_gdb = should_attach_gdb(request);