[CRIU] [PATCH v4 07/19] sfds: Protect service fds reuse

[Kirill Tkhai]

This patch introduces sfds_protected, which allows
to mask areas, where modifications of sfds are prohibited.
That guarantees, that populated sfds won't be reused.

v4: New

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 criu/include/servicefd.h |    1 +
 criu/util.c              |   13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/criu/include/servicefd.h b/criu/include/servicefd.h
index 6266b5324..812396310 100644
--- a/criu/include/servicefd.h
+++ b/criu/include/servicefd.h
@@ -27,6 +27,7 @@ enum sfd_type {
 };
 
 struct pstree_item;
+extern bool sfds_protected;
 
 extern void set_proc_self_fd(int fd);
 extern int clone_service_fd(int id);
diff --git a/criu/util.c b/criu/util.c
index d90bab09c..c3665f10b 100644
--- a/criu/util.c
+++ b/criu/util.c
@@ -473,12 +473,22 @@ int service_fd_min_fd(struct pstree_item *item)
 }
 
 static DECLARE_BITMAP(sfd_map, SERVICE_FD_MAX);
+bool sfds_protected = false;
+
+static void sfds_protection_bug(void)
+{
+	pr_err("Service fd is being modified in protected context\n");
+	print_stack_trace(current ? vpid(current) : 0);
+	BUG();
+}
 
 int install_service_fd(enum sfd_type type, int fd)
 {
 	int sfd = __get_service_fd(type, service_fd_id);
 
 	BUG_ON((int)type <= SERVICE_FD_MIN || (int)type >= SERVICE_FD_MAX);
+	if (sfds_protected && !test_bit(type, sfd_map))
+		sfds_protection_bug();
 
 	if (dup3(fd, sfd, O_CLOEXEC) != sfd) {
 		pr_perror("Dup %d -> %d failed", fd, sfd);
@@ -508,6 +518,9 @@ int close_service_fd(enum sfd_type type)
 {
 	int fd;
 
+	if (sfds_protected)
+		sfds_protection_bug();
+
 	fd = get_service_fd(type);
 	if (fd < 0)
 		return 0;