Revert 270173 "Remove SCM_CREDENTIALS fallback code from breakpad"

trunk/src/base/linux_util.cc

Index: trunk/src/base/linux_util.cc
===================================================================
--- trunk/src/base/linux_util.cc	(revision 270276)
+++ trunk/src/base/linux_util.cc	(working copy)
@@ -71,6 +71,55 @@
 };
 #endif  // if defined(OS_LINUX)
 
+// expected prefix of the target of the /proc/self/fd/%d link for a socket
+const char kSocketLinkPrefix[] = "socket:[";
+
+// Parse a symlink in /proc/pid/fd/$x and return the inode number of the
+// socket.
+//   inode_out: (output) set to the inode number on success
+//   path: e.g. /proc/1234/fd/5 (must be a UNIX domain socket descriptor)
+//   log: if true, log messages about failure details
+bool ProcPathGetInode(ino_t* inode_out, const char* path, bool log = false) {
+  DCHECK(inode_out);
+  DCHECK(path);
+
+  char buf[256];
+  const ssize_t n = readlink(path, buf, sizeof(buf) - 1);
+  if (n == -1) {
+    if (log) {
+      DLOG(WARNING) << "Failed to read the inode number for a socket from /proc"
+                      "(" << errno << ")";
+    }
+    return false;
+  }
+  buf[n] = 0;
+
+  if (memcmp(kSocketLinkPrefix, buf, sizeof(kSocketLinkPrefix) - 1)) {
+    if (log) {
+      DLOG(WARNING) << "The descriptor passed from the crashing process wasn't "
+                      " a UNIX domain socket.";
+    }
+    return false;
+  }
+
+  char* endptr;
+  const unsigned long long int inode_ul =
+      strtoull(buf + sizeof(kSocketLinkPrefix) - 1, &endptr, 10);
+  if (*endptr != ']')
+    return false;
+
+  if (inode_ul == ULLONG_MAX) {
+    if (log) {
+      DLOG(WARNING) << "Failed to parse a socket's inode number: the number "
+                       "was too large. Please report this bug: " << buf;
+    }
+    return false;
+  }
+
+  *inode_out = inode_ul;
+  return true;
+}
+
 }  // namespace
 
 namespace base {
@@ -129,6 +178,78 @@
   base::strlcpy(g_linux_distro, trimmed_distro.c_str(), kDistroSize);
 }
 
+bool FileDescriptorGetInode(ino_t* inode_out, int fd) {
+  DCHECK(inode_out);
+
+  struct stat buf;
+  if (fstat(fd, &buf) < 0)
+    return false;
+
+  if (!S_ISSOCK(buf.st_mode))
+    return false;
+
+  *inode_out = buf.st_ino;
+  return true;
+}
+
+bool FindProcessHoldingSocket(pid_t* pid_out, ino_t socket_inode) {
+  DCHECK(pid_out);
+  bool already_found = false;
+
+  DIR* proc = opendir("/proc");
+  if (!proc) {
+    DLOG(WARNING) << "Cannot open /proc";
+    return false;
+  }
+
+  std::vector<pid_t> pids;
+
+  struct dirent* dent;
+  while ((dent = readdir(proc))) {
+    char* endptr;
+    const unsigned long int pid_ul = strtoul(dent->d_name, &endptr, 10);
+    if (pid_ul == ULONG_MAX || *endptr)
+      continue;
+    pids.push_back(pid_ul);
+  }
+  closedir(proc);
+
+  for (std::vector<pid_t>::const_iterator
+       i = pids.begin(); i != pids.end(); ++i) {
+    const pid_t current_pid = *i;
+    char buf[256];
+    snprintf(buf, sizeof(buf), "/proc/%d/fd", current_pid);
+    DIR* fd = opendir(buf);
+    if (!fd)
+      continue;
+
+    while ((dent = readdir(fd))) {
+      if (snprintf(buf, sizeof(buf), "/proc/%d/fd/%s", current_pid,
+                   dent->d_name) >= static_cast<int>(sizeof(buf))) {
+        continue;
+      }
+
+      ino_t fd_inode = static_cast<ino_t>(-1);
+      if (ProcPathGetInode(&fd_inode, buf)) {
+        if (fd_inode == socket_inode) {
+          if (already_found) {
+            closedir(fd);
+            return false;
+          }
+
+          already_found = true;
+          *pid_out = current_pid;
+          break;
+        }
+      }
+    }
+
+    closedir(fd);
+  }
+
+  return already_found;
+}
+
 pid_t FindThreadIDWithSyscall(pid_t pid, const std::string& expected_data,
                               bool* syscall_supported) {
   char buf[256];