Revert 270173 "Remove SCM_CREDENTIALS fallback code from breakpad"

trunk/src/components/breakpad/browser/crash_handler_host_linux.cc

Index: trunk/src/components/breakpad/browser/crash_handler_host_linux.cc
===================================================================
--- trunk/src/components/breakpad/browser/crash_handler_host_linux.cc	(revision 270276)
+++ trunk/src/components/breakpad/browser/crash_handler_host_linux.cc	(working copy)
@@ -219,6 +219,7 @@
 
   // Walk the control payload an extract the file descriptor and validated pid.
   pid_t crashing_pid = -1;
+  int partner_fd = -1;
   int signal_fd = -1;
   for (struct cmsghdr *hdr = CMSG_FIRSTHDR(&msg); hdr;
        hdr = CMSG_NXTHDR(&msg, hdr)) {
@@ -229,7 +230,7 @@
           (((uint8_t*)CMSG_DATA(hdr)) - (uint8_t*)hdr);
       DCHECK_EQ(len % sizeof(int), 0u);
       const unsigned num_fds = len / sizeof(int);
-      if (num_fds != 1) {
+      if (num_fds != 2) {
         // A nasty process could try and send us too many descriptors and
         // force a leak.
         LOG(ERROR) << "Death signal contained wrong number of descriptors;"
@@ -238,7 +239,8 @@
           close(reinterpret_cast<int*>(CMSG_DATA(hdr))[i]);
         return;
       } else {
-        signal_fd = reinterpret_cast<int*>(CMSG_DATA(hdr))[0];
+        partner_fd = reinterpret_cast<int*>(CMSG_DATA(hdr))[0];
+        signal_fd = reinterpret_cast<int*>(CMSG_DATA(hdr))[1];
       }
     } else if (hdr->cmsg_type == SCM_CREDENTIALS) {
       const struct ucred *cred =
@@ -247,14 +249,46 @@
     }
   }
 
-  if (crashing_pid == -1 || signal_fd == -1) {
+  if (crashing_pid == -1 || partner_fd == -1 || signal_fd == -1) {
     LOG(ERROR) << "Death signal message didn't contain all expected control"
                << " messages";
+    if (partner_fd >= 0)
+      close(partner_fd);
     if (signal_fd >= 0)
       close(signal_fd);
     return;
   }
 
+  // Kernel bug workaround (broken in 2.6.30 and 2.6.32, working in 2.6.38).
+  // The kernel doesn't translate PIDs in SCM_CREDENTIALS across PID
+  // namespaces. Thus |crashing_pid| might be garbage from our point of view.
+  // In the future we can remove this workaround, but we have to wait a couple
+  // of years to be sure that it's worked its way out into the world.
+  // TODO(thestig) Remove the workaround when Ubuntu Lucid is deprecated.
+
+  // The crashing process closes its copy of the signal_fd immediately after
+  // calling sendmsg(). We can thus not reliably look for with with
+  // FindProcessHoldingSocket(). But by necessity, it has to keep the
+  // partner_fd open until the crashdump is complete.
+  ino_t inode_number;
+  if (!base::FileDescriptorGetInode(&inode_number, partner_fd)) {
+    LOG(WARNING) << "Failed to get inode number for passed socket";
+    close(partner_fd);
+    close(signal_fd);
+    return;
+  }
+  close(partner_fd);
+
+  pid_t actual_crashing_pid = -1;
+  if (!base::FindProcessHoldingSocket(&actual_crashing_pid, inode_number)) {
+    LOG(WARNING) << "Failed to find process holding other end of crash reply "
+                    "socket";
+    close(signal_fd);
+    return;
+  }
+
+  crashing_pid = actual_crashing_pid;
+
   // The crashing TID set inside the compromised context via
   // sys_gettid() in ExceptionHandler::HandleSignal might be wrong (if
   // the kernel supports PID namespacing) and may need to be