Fix recursive deadlock in sandbox::InitLibcLocaltimeFunctions

QtWebEngineProcess overrides the C library's localtime* functions by redefining
the symbols in src/process/main.cpp and then using dlsym(RTLD_NEXT, ...) to
fetch the original symbols in //sandbox/linux/services/libc_interceptor.cc. The
functions InitLibcLocaltimeFunctions{,Impl} use pthread_once to guarantee that
this symbol resolution happens only once.

If dlsym fails, for example because the C library is earlier in the search path
than QtWebEngineCore, then InitLibcLocaltimeFunctionsImpl tries to print an
error message with LOG(ERROR). However, printing a log message involves also
printing the timestamp in the local time zone, using, of course, localtime_r.
Thus, InitLibcLocaltimeFunctions depends on localtime_r depends on
InitLibcLocaltimeFunctions, and we get a deadlock due to the recursive use of
pthread_once.

This deadlock happens only for utility processes and not for zygotes or
renderers, since the latter proxy the localtime* calls back to the main process.
(See service_manager::ZygoteMain, where the first function call is to
sandbox::SetAmZygoteOrRenderer, and compare with content::UtilityMain)

Task-number: QTBUG-82186
Change-Id: I32009e8482b2634c47082a4c89393dc61c22507e
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/chromium/sandbox/linux/services/libc_interceptor.cc b/chromium/sandbox/linux/services/libc_interceptor.cc
index ed4dd02473a..fad77f9b5f0 100644
--- a/chromium/sandbox/linux/services/libc_interceptor.cc
+++ b/chromium/sandbox/linux/services/libc_interceptor.cc
@@ -199,6 +199,7 @@ static void InitLibcLocaltimeFunctionsImpl() {
   g_libc_funcs->localtime64_r =
       reinterpret_cast<LocaltimeRFunction>(dlsym(RTLD_NEXT, "localtime64_r"));
 
+#if !defined(TOOLKIT_QT)
   if (!g_libc_funcs->localtime || !g_libc_funcs->localtime_r) {
     // https://bugs.chromium.org/p/chromium/issues/detail?id=16800
     //
@@ -210,6 +211,7 @@ static void InitLibcLocaltimeFunctionsImpl() {
                   " time related functions to misbehave. "
                   "https://bugs.chromium.org/p/chromium/issues/detail?id=16800";
   }
+#endif
 
   if (!g_libc_funcs->localtime)
     g_libc_funcs->localtime = gmtime;