Redirect fopen("/dev/urandom") so that NSS can properly seed it's RNG.

content/browser/zygote_main_linux.cc

Index: content/browser/zygote_main_linux.cc
diff --git a/content/browser/zygote_main_linux.cc b/content/browser/zygote_main_linux.cc
index 020d7771ca6ed9cfe8351dcba1098d10b8a47f84..cb1cda5532eed7c1f285df86db7bc67fec4db58d 100644
--- a/content/browser/zygote_main_linux.cc
+++ b/content/browser/zygote_main_linux.cc
@@ -7,6 +7,7 @@
 #include <dlfcn.h>
 #include <fcntl.h>
 #include <pthread.h>
+#include <stdio.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -25,6 +26,7 @@
 #include "base/pickle.h"
 #include "base/process_util.h"
 #include "base/rand_util.h"
+#include "base/rand_util_c.h"
 #include "base/sys_info.h"
 #include "build/build_config.h"
 #include "crypto/nss_util.h"
@@ -64,6 +66,8 @@ static const int kMagicSandboxIPCDescriptor = 5;
 static const int kZygoteIdDescriptor = 7;
 static bool g_suid_sandbox_active = false;
 
+static char kUrandomDevPath[] = "/dev/urandom";

[agl, 2012/04/10 15:18:13]

const

[Sergey Ulanov, 2012/04/10 17:21:01]

Done.

+
 #if defined(SECCOMP_SANDBOX)
 static int g_proc_fd = -1;
 #endif
@@ -632,11 +636,16 @@ static bool g_am_zygote_or_renderer = false;
 typedef struct tm* (*LocaltimeFunction)(const time_t* timep);
 typedef struct tm* (*LocaltimeRFunction)(const time_t* timep,
                                          struct tm* result);
+typedef FILE* (*FopenFunction)(const char* path, const char* mode);
 
 static pthread_once_t g_libc_localtime_funcs_guard = PTHREAD_ONCE_INIT;
 static LocaltimeFunction g_libc_localtime;
 static LocaltimeRFunction g_libc_localtime_r;
 
+static pthread_once_t g_libc_fopen_funcs_guard = PTHREAD_ONCE_INIT;
+static FopenFunction g_libc_fopen;
+static FopenFunction g_libc_fopen64;
+
 static void InitLibcLocaltimeFunctions() {
   g_libc_localtime = reinterpret_cast<LocaltimeFunction>(
                          dlsym(RTLD_NEXT, "localtime"));
@@ -686,6 +695,61 @@ struct tm* localtime_r(const time_t* timep, struct tm* result) {
   }
 }
 
+static void InitLibcFopenFunctions() {
+  g_libc_fopen = reinterpret_cast<FopenFunction>(
+                         dlsym(RTLD_NEXT, "fopen"));

[agl, 2012/04/10 15:18:13]

nit: indentation here should be four spaces from the start of the previous line
I think. Same a couple of lines down.

[Sergey Ulanov, 2012/04/10 17:21:01]

Done.

+  g_libc_fopen64 = reinterpret_cast<FopenFunction>(
+                         dlsym(RTLD_NEXT, "fopen64"));
+
+  if (!g_libc_fopen || !g_libc_fopen64) {
+    LOG(ERROR) << "Failed to get fopen() from glibc.";
+  }
+}
+
+// fopen() and fopen64() are intercepted here so that NSS can open
+// /dev/urandom to seed it's random number generator. NSS is used by
+// remoting in the sendbox.
+
+// fopen() call may be redirected to fopen64() in stdio.h using
+// __REDIRECT(), which sets asm name for fopen() to "fopen64". This
+// means that we cannot override fopen() directly here. Instead the
+// the code below defines fopen_override() function with asm name
+// "fopen", so that all references to fopen() will resolve to this
+// function.
+__attribute__ ((__visibility__("default")))
+FILE* fopen_override(const char* path, const char* mode)  __asm__ ("fopen");

[agl, 2012/04/10 15:18:13]

nit: blank line between these.

[Sergey Ulanov, 2012/04/10 17:21:01]

Done.

+__attribute__ ((__visibility__("default")))
+FILE* fopen_override(const char* path, const char* mode) {
+  if (g_am_zygote_or_renderer && strcmp(path, kUrandomDevPath) == 0) {
+    int fd = dup(GetUrandomFD());

[agl, 2012/04/10 15:18:13]

needs to be wrapped with HANDLE_EINTR

[Sergey Ulanov, 2012/04/10 17:21:01]

Done.

+    if (fd < 0) {
+      LOG(ERROR) << "dup() failed.";

[agl, 2012/04/10 15:18:13]

PLOG

[Sergey Ulanov, 2012/04/10 17:21:01]

Done.

+      return NULL;
+    }
+    return fdopen(fd, mode);
+  } else {
+    CHECK_EQ(0, pthread_once(&g_libc_fopen_funcs_guard,
+                             InitLibcFopenFunctions));
+    return g_libc_fopen(path, mode);
+  }
+}
+
+__attribute__ ((__visibility__("default")))
+FILE* fopen64(const char* path, const char* mode) {
+  if (g_am_zygote_or_renderer && strcmp(path, kUrandomDevPath) == 0) {
+    int fd = dup(GetUrandomFD());

[agl, 2012/04/10 15:18:13]

needs to be wrapped with HANDLE_EINTR

[Sergey Ulanov, 2012/04/10 17:21:01]

Done.

+    if (fd < 0) {
+      PLOG(ERROR) << "dup() failed.";
+      return NULL;
+    }
+    return fdopen(fd, mode);
+  } else {
+    CHECK_EQ(0, pthread_once(&g_libc_fopen_funcs_guard,
+                             InitLibcFopenFunctions));
+    return g_libc_fopen64(path, mode);
+  }
+}
+
 #endif  // !CHROMIUM_SELINUX
 
 // This function triggers the static and lazy construction of objects that need