virtiofsd needs access to /proc/self/fd. Let's move to a new pid
namespace so that a compromised process cannot see another other
processes running on the system.
One wrinkle in this approach: unshare(CLONE_NEWPID) affects *child*
processes and not the current process. Therefore we need to fork the
pid 1 process that will actually run virtiofsd and leave a parent in
waitpid(2). This is not the same thing as daemonization and parent
processes should not notice a difference.
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
contrib/virtiofsd/passthrough_ll.c | 95 ++++++++++++++++++++++--------
1 file changed, 72 insertions(+), 23 deletions(-)
diff --git a/contrib/virtiofsd/passthrough_ll.c
b/contrib/virtiofsd/passthrough_ll.c
index c27ff7d800..b6ee9b2e90 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -56,9 +56,12 @@
#include <sys/xattr.h>
#include <sys/mman.h>
#include <sys/socket.h>
+#include <sys/types.h>
#include <sys/un.h>
+#include <sys/wait.h>
#include <sys/capability.h>
+
#include "ireg.h"
#include <sys/mount.h>
#include <sys/resource.h>
@@ -2749,6 +2752,72 @@ static void setup_net_namespace(void)
}
}
+/*
+ * Move to a new pid namespace to prevent access to other processes if this
+ * process is compromised.
+ */
+static void setup_pid_namespace(void)
+{
+ pid_t child;
+
+ /*
+ * Create a new pid namespace for *child* processes. We'll have to
+ * fork in order to enter the new pid namespace. A new mount namespace
+ * is also needed so that we can remount /proc for the new pid
+ * namespace.
+ */
+ if (unshare(CLONE_NEWPID | CLONE_NEWNS) != 0) {
+ fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWPID | CLONE_NEWNS):
%m\n");
+ exit(1);
+ }
+
+ child = fork();
+ if (child < 0) {
+ fuse_log(FUSE_LOG_ERR, "fork() failed: %m\n");
+ exit(1);
+ }
+ if (child > 0) {
+ pid_t waited;
+ int wstatus;
+
+ /* The parent waits for the child */
+ do {
+ waited = waitpid(child, &wstatus, 0);
+ } while (waited < 0 && errno == EINTR);
+
+ if (WIFEXITED(wstatus)) {
+ exit(WEXITSTATUS(wstatus));
+ }
+
+ exit(1);
+ }
+
+ /*
+ * If the mounts have shared propagation then we want to opt out so our
+ * mount changes don't affect the parent mount namespace.
+ */
+ if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
+ fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_SLAVE): %m\n");
+ exit(1);
+ }
+
+ /* The child must remount /proc to use the new pid namespace */
+ if (mount("proc", "/proc", "proc",
+ MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, NULL) < 0) {
+ fuse_log(FUSE_LOG_ERR, "mount(/proc): %m\n");
+ exit(1);
+ }
+}
+
+static void setup_proc_self_fd(struct lo_data *lo)
+{
+ lo->proc_self_fd = open("/proc/self/fd", O_PATH);
+ if (lo->proc_self_fd == -1) {
+ fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
+ exit(1);
+ }
+}
+
/* This magic is based on lxc's lxc_pivot_root() */
static void setup_pivot_root(const char *source)
{
@@ -2803,20 +2872,10 @@ static void setup_pivot_root(const char *source)
/*
* Make the source directory our root so symlinks cannot escape and no other
- * files are accessible.
+ * files are accessible. Assumes unshare(CLONE_NEWNS) was already called.
*/
static void setup_mount_namespace(const char *source)
{
- if (unshare(CLONE_NEWNS) != 0) {
- fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWNS): %m\n");
- exit(1);
- }
-
- if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
- fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_PRIVATE): %m\n");
- exit(1);
- }
-
if (mount(source, source, NULL, MS_BIND, NULL) < 0) {
fuse_log(FUSE_LOG_ERR, "mount(%s, %s, MS_BIND): %m\n", source,
source);
exit(1);
@@ -2831,6 +2890,8 @@ static void setup_mount_namespace(const char *source)
*/
static void setup_sandbox(struct lo_data *lo, bool enable_syslog)
{
+ setup_pid_namespace();
+ setup_proc_self_fd(lo);
setup_net_namespace();
setup_mount_namespace(lo->source);
setup_seccomp(enable_syslog);
@@ -2860,15 +2921,6 @@ static void setup_root(struct lo_data *lo, struct
lo_inode *root)
g_atomic_int_set(&root->refcount, 2);
}
-static void setup_proc_self_fd(struct lo_data *lo)
-{
- lo->proc_self_fd = open("/proc/self/fd", O_PATH);
- if (lo->proc_self_fd == -1) {
- fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
- exit(1);
- }
-}
-
/* Raise the maximum number of open file descriptors to the system limit */
static void setup_nofile_rlimit(void)
{
@@ -3110,9 +3162,6 @@ int main(int argc, char *argv[])
get_shared(&lo, &lo.root);
}
- /* Must be after daemonize to get the right /proc/self/fd */
- setup_proc_self_fd(&lo);
-
setup_sandbox(&lo, opts.syslog);
setup_root(&lo, &lo.root);
--
2.21.0
