Allow Linux dumper to work on PTRACE-hardened kernels

A=Chris Coulson <chris.coulson@canonical.com>
R=nealsid at http://breakpad.appspot.com/166001/show

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@673 4c0a9323-5329-0410-9bdc-e9ce6186880e
This commit is contained in:
ted.mielczarek 2010-08-27 13:18:49 +00:00
parent 8e77c078d6
commit 662b6da59d
2 changed files with 69 additions and 0 deletions

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@ -89,6 +89,11 @@
#include "common/linux/memory.h"
#include "client/linux/minidump_writer/minidump_writer.h"
#include "common/linux/guid_creator.h"
#include "common/linux/eintr_wrapper.h"
#ifndef PR_SET_PTRACER
#define PR_SET_PTRACER 0x59616d61
#endif
// A wrapper for the tgkill syscall: send a signal to a specific thread.
static int tgkill(pid_t tgid, pid_t tid, int sig) {
@ -301,6 +306,11 @@ struct ThreadArgument {
// static
int ExceptionHandler::ThreadEntry(void *arg) {
const ThreadArgument *thread_arg = reinterpret_cast<ThreadArgument*>(arg);
// Block here until the crashing process unblocks us when
// we're allowed to use ptrace
thread_arg->handler->WaitForContinueSignal();
return thread_arg->handler->DoDump(thread_arg->pid, thread_arg->context,
thread_arg->context_size) == false;
}
@ -355,14 +365,35 @@ bool ExceptionHandler::GenerateDump(CrashContext *context) {
thread_arg.context = context;
thread_arg.context_size = sizeof(*context);
// We need to explicitly enable ptrace of parent processes on some
// kernels, but we need to know the PID of the cloned process before we
// can do this. Create a pipe here which we can use to block the
// cloned process after creating it, until we have explicitly enabled ptrace
if(sys_pipe(fdes) == -1) {
// Creating the pipe failed. We'll log an error but carry on anyway,
// as we'll probably still get a useful crash report. All that will happen
// is the write() and read() calls will fail with EBADF
static const char no_pipe_msg[] = "ExceptionHandler::GenerateDump \
sys_pipe failed:";
sys_write(2, no_pipe_msg, sizeof(no_pipe_msg) - 1);
sys_write(2, strerror(errno), strlen(strerror(errno)));
sys_write(2, "\n", 1);
}
const pid_t child = sys_clone(
ThreadEntry, stack, CLONE_FILES | CLONE_FS | CLONE_UNTRACED,
&thread_arg, NULL, NULL, NULL);
int r, status;
// Allow the child to ptrace us
prctl(PR_SET_PTRACER, child, 0, 0, 0);
SendContinueSignalToChild();
do {
r = sys_waitpid(child, &status, __WALL);
} while (r == -1 && errno == EINTR);
sys_close(fdes[0]);
sys_close(fdes[1]);
if (r == -1) {
static const char msg[] = "ExceptionHandler::GenerateDump waitpid failed:";
sys_write(2, msg, sizeof(msg) - 1);
@ -379,6 +410,35 @@ bool ExceptionHandler::GenerateDump(CrashContext *context) {
return success;
}
// This function runs in a compromised context: see the top of the file.
void ExceptionHandler::SendContinueSignalToChild() {
static const char okToContinueMessage = 'a';
int r;
r = HANDLE_EINTR(sys_write(fdes[1], &okToContinueMessage, sizeof(char)));
if(r == -1) {
static const char msg[] = "ExceptionHandler::SendContinueSignalToChild \
sys_write failed:";
sys_write(2, msg, sizeof(msg) - 1);
sys_write(2, strerror(errno), strlen(strerror(errno)));
sys_write(2, "\n", 1);
}
}
// This function runs in a compromised context: see the top of the file.
// Runs on the cloned process.
void ExceptionHandler::WaitForContinueSignal() {
int r;
char receivedMessage;
r = HANDLE_EINTR(sys_read(fdes[0], &receivedMessage, sizeof(char)));
if(r == -1) {
static const char msg[] = "ExceptionHandler::WaitForContinueSignal \
sys_read failed:";
sys_write(2, msg, sizeof(msg) - 1);
sys_write(2, strerror(errno), strlen(strerror(errno)));
sys_write(2, "\n", 1);
}
}
// This function runs in a compromised context: see the top of the file.
// Runs on the cloned process.
bool ExceptionHandler::DoDump(pid_t crashing_process, const void* context,

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@ -184,6 +184,8 @@ class ExceptionHandler {
void UninstallHandlers();
void PreresolveSymbols();
bool GenerateDump(CrashContext *context);
void SendContinueSignalToChild();
void WaitForContinueSignal();
void UpdateNextID();
static void SignalHandler(int sig, siginfo_t* info, void* uc);
@ -223,6 +225,13 @@ class ExceptionHandler {
// A vector of the old signal handlers.
std::vector<std::pair<int, struct sigaction *> > old_handlers_;
// We need to explicitly enable ptrace of parent processes on some
// kernels, but we need to know the PID of the cloned process before we
// can do this. We create a pipe which we can use to block the
// cloned process after creating it, until we have explicitly enabled
// ptrace. This is used to store the file descriptors for the pipe
int fdes[2];
};
} // namespace google_breakpad