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..860d7ec5df2f7ae229b5770cbed4e28b2c3ce254 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"
@@ -632,11 +634,16 @@ 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 +693,50 @@ struct tm* localtime_r(const time_t* timep, struct tm* result) {
   }
 }
 
+static void InitLibcFopenFunctions() {
+  g_libc_fopen = reinterpret_cast<FopenFunction>(
+                         dlsym(RTLD_NEXT, "fopen"));
+  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.";
+  }
+}
+
+__attribute__ ((__visibility__("default")))
+FILE* fopen(const char* path, const char* mode)  __asm__ ("fopen");
+FILE* fopen(const char* path, const char* mode) {
+  if (g_am_zygote_or_renderer && strcmp(path, "/dev/urandom") == 0) {

[Ben Chan, 2012/04/10 02:17:15]

static const char kDevUrandomFile[] = "/dev/urandom";

strncmp(path, kDevUrandomFile, sizeof(kDevUrandomFile)) == 0

[Sergey Ulanov, 2012/04/10 03:02:53]

How would that be better than strcmp()? It would also match /dev/urandom0, etc.
Is that what we want?

[Ben Chan, 2012/04/10 03:24:41]

strcmp should be fine. But I think it's still good to define kDevUrandomFile[],
probably exposed from URandomFD.

[Sergey Ulanov, 2012/04/10 06:03:38]

Done.

+    int fd = dup(GetUrandomFD());
+    if (fd < 0) {
+      LOG(ERROR) << "dup() failed.";
+      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, "/dev/urandom") == 0) {
+    int fd = dup(GetUrandomFD());
+    if (fd < 0) {
+      PLOG(ERROR) << "dup() failed.";
+      return NULL;
+    }
+     return fdopen(fd, mode);

[Ben Chan, 2012/04/10 02:17:15]

indentation

[Sergey Ulanov, 2012/04/10 03:02:53]

Done.

+  } 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