From 52a20dc78a372394471e3394a8d335ef00cebad3 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 7 Nov 2017 15:33:40 -0500
Subject: [PATCH] Fix: liblttng-ust-fd.so: override fclose symbol

fclose() invoked from application or libraries end up calling close()
from within the libc, which bypasses our file descriptor tracking.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 include/ust-fd.h                         |  3 +++
 liblttng-ust-comm/lttng-ust-fd-tracker.c | 32 ++++++++++++++++++++++++
 liblttng-ust-fd/lttng-ust-fd.c           | 25 ++++++++++++++++++
 3 files changed, 60 insertions(+)

diff --git a/include/ust-fd.h b/include/ust-fd.h
index 7cbcf47c..032cac53 100644
--- a/include/ust-fd.h
+++ b/include/ust-fd.h
@@ -24,6 +24,8 @@
  * These declarations should NOT be considered stable API.
  */
 
+#include <stdio.h>
+
 void lttng_ust_init_fd_tracker(void);
 void lttng_ust_add_fd_to_tracker(int fd);
 void lttng_ust_delete_fd_from_tracker(int fd);
@@ -31,6 +33,7 @@ void lttng_ust_lock_fd_tracker(void);
 void lttng_ust_unlock_fd_tracker(void);
 
 int lttng_ust_safe_close_fd(int fd, int (*close_cb)(int));
+int lttng_ust_safe_fclose_stream(FILE *stream, int (*fclose_cb)(FILE *stream));
 int lttng_ust_safe_closefrom_fd(int lowfd, int (*close_cb)(int));
 
 #endif	/* _LTTNG_UST_FD_H */
diff --git a/liblttng-ust-comm/lttng-ust-fd-tracker.c b/liblttng-ust-comm/lttng-ust-fd-tracker.c
index 5a763ff2..d56288e3 100644
--- a/liblttng-ust-comm/lttng-ust-fd-tracker.c
+++ b/liblttng-ust-comm/lttng-ust-fd-tracker.c
@@ -197,6 +197,38 @@ int lttng_ust_safe_close_fd(int fd, int (*close_cb)(int fd))
 	return ret;
 }
 
+/*
+ * Interface allowing applications to close arbitrary streams.
+ * We check if it is owned by lttng-ust, and return -1, errno=EBADF
+ * instead of closing it if it is the case.
+ */
+int lttng_ust_safe_fclose_stream(FILE *stream, int (*fclose_cb)(FILE *stream))
+{
+	int ret = 0, fd;
+
+	lttng_ust_fixup_fd_tracker_tls();
+
+	/*
+	 * If called from lttng-ust, we directly call fclose without
+	 * validating whether the FD is part of the tracked set.
+	 */
+	if (URCU_TLS(thread_fd_tracking))
+		return fclose_cb(stream);
+
+	fd = fileno(stream);
+
+	lttng_ust_lock_fd_tracker();
+	if (IS_FD_VALID(fd) && IS_FD_SET(fd, lttng_fd_set)) {
+		ret = -1;
+		errno = EBADF;
+	} else {
+		ret = fclose_cb(stream);
+	}
+	lttng_ust_unlock_fd_tracker();
+
+	return ret;
+}
+
 #ifdef __OpenBSD__
 static void set_close_success(int *p)
 {
diff --git a/liblttng-ust-fd/lttng-ust-fd.c b/liblttng-ust-fd/lttng-ust-fd.c
index 6a095db6..863f0618 100644
--- a/liblttng-ust-fd/lttng-ust-fd.c
+++ b/liblttng-ust-fd/lttng-ust-fd.c
@@ -31,6 +31,7 @@
 volatile enum ust_loglevel ust_loglevel;
 
 static int (*__lttng_ust_fd_plibc_close)(int fd);
+static int (*__lttng_ust_fd_plibc_fclose)(FILE *stream);
 
 static
 int _lttng_ust_fd_libc_close(int fd)
@@ -45,11 +46,35 @@ int _lttng_ust_fd_libc_close(int fd)
 	return lttng_ust_safe_close_fd(fd, __lttng_ust_fd_plibc_close);
 }
 
+static
+int _lttng_ust_fd_libc_fclose(FILE *stream)
+{
+	if (!__lttng_ust_fd_plibc_fclose) {
+		__lttng_ust_fd_plibc_fclose = dlsym(RTLD_NEXT, "fclose");
+		if (!__lttng_ust_fd_plibc_fclose) {
+			fprintf(stderr, "%s\n", dlerror());
+			return -1;
+		}
+	}
+	return lttng_ust_safe_fclose_stream(stream,
+			__lttng_ust_fd_plibc_fclose);
+}
+
 int close(int fd)
 {
 	return _lttng_ust_fd_libc_close(fd);
 }
 
+/*
+ * Note: fcloseall() is not an issue because it fcloses only the
+ * streams it knows about, which differs from the problems caused by
+ * gnulib close_stdout(), which does an explicit fclose(stdout).
+ */
+int fclose(FILE *stream)
+{
+	return _lttng_ust_fd_libc_fclose(stream);
+}
+
 #if defined(__sun__) || defined(__FreeBSD__)
 /* Solaris and FreeBSD. */
 void closefrom(int lowfd)
-- 
2.34.1