Fall back to FD_CLOEXEC when O_CLOEXEC is unavailable.

Older Linux systems don't have O_CLOEXEC.  If that's the case, we fcntl
immediately after open, to minimize the length of the racy period in
which an
operation in another thread can leak a file descriptor to a child.

2 files changed, 28 insertions, 5 deletions

diff --git a/src/pages.c b/src/pages.c
index fec64dd..0883647 100644
--- a/src/pages.c
+++ b/src/pages.c
@@ -353,14 +353,31 @@ os_overcommits_proc(void) {
 	ssize_t nread;
 
 #if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_open)
-	fd = (int)syscall(SYS_open, "/proc/sys/vm/overcommit_memory", O_RDONLY |
-	    O_CLOEXEC);
+	#if defined(O_CLOEXEC)
+		fd = (int)syscall(SYS_open, "/proc/sys/vm/overcommit_memory", O_RDONLY |
+			O_CLOEXEC);
+	#else
+		fd = (int)syscall(SYS_open, "/proc/sys/vm/overcommit_memory", O_RDONLY);
+		fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
+	#endif
 #elif defined(JEMALLOC_USE_SYSCALL) && defined(SYS_openat)
-	fd = (int)syscall(SYS_openat,
-	    AT_FDCWD, "/proc/sys/vm/overcommit_memory", O_RDONLY | O_CLOEXEC);
+	#if defined(O_CLOEXEC)
+		fd = (int)syscall(SYS_openat,
+			AT_FDCWD, "/proc/sys/vm/overcommit_memory", O_RDONLY | O_CLOEXEC);
+	#else
+		fd = (int)syscall(SYS_openat,
+			AT_FDCWD, "/proc/sys/vm/overcommit_memory", O_RDONLY);
+		fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
+	#endif
 #else
-	fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY | O_CLOEXEC);
+	#if defined(O_CLOEXEC)
+		fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY | O_CLOEXEC);
+	#else
+		fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY);
+		fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
+	#endif
 #endif
+
 	if (fd == -1) {
 		return false; /* Error. */
 	}
diff --git a/src/prof.c b/src/prof.c
index 975722c..a1ca9e2 100644
--- a/src/prof.c
+++ b/src/prof.c
@@ -1409,7 +1409,13 @@ prof_open_maps(const char *format, ...) {
 	va_start(ap, format);
 	malloc_vsnprintf(filename, sizeof(filename), format, ap);
 	va_end(ap);
+
+#if defined(O_CLOEXEC)
 	mfd = open(filename, O_RDONLY | O_CLOEXEC);
+#else
+	mfd = open(filename, O_RDONLY);
+	fcntl(mfd, F_SETFD, fcntl(mfd, F_GETFD) | FD_CLOEXEC);
+#endif
 
 	return mfd;
 }