From a7a87a751a9893830d031a957a751b7622b71fb2 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Mon, 27 Jan 2020 19:01:29 +0100 Subject: [PATCH 058/116] virtiofsd: move to a new pid namespace MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Dr. David Alan Gilbert Message-id: <20200127190227.40942-55-dgilbert@redhat.com> Patchwork-id: 93510 O-Subject: [RHEL-AV-8.2 qemu-kvm PATCH 054/112] virtiofsd: move to a new pid namespace Bugzilla: 1694164 RH-Acked-by: Philippe Mathieu-Daudé RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Sergio Lopez Pascual From: Stefan Hajnoczi 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 Reviewed-by: Daniel P. Berrangé Signed-off-by: Dr. David Alan Gilbert (cherry picked from commit 8e1d4ef231d8327be219f7aea7aa15d181375bbc) Signed-off-by: Miroslav Rezanina --- tools/virtiofsd/passthrough_ll.c | 134 +++++++++++++++++++++++++-------------- 1 file changed, 86 insertions(+), 48 deletions(-) diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 27ab328..0947d14 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -51,7 +51,10 @@ #include #include #include +#include #include +#include +#include #include #include @@ -1945,24 +1948,95 @@ static void print_capabilities(void) } /* - * Called after our UNIX domain sockets have been created, now we can move to - * an empty network namespace to prevent TCP/IP and other network activity in - * case this process is compromised. + * Move to a new mount, net, and pid namespaces to isolate this process. */ -static void setup_net_namespace(void) +static void setup_namespaces(struct lo_data *lo, struct fuse_session *se) { - if (unshare(CLONE_NEWNET) != 0) { - fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWNET): %m\n"); + 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. + * + * Our UNIX domain sockets have been created. Now we can move to + * an empty network namespace to prevent TCP/IP and other network + * activity in case this process is compromised. + */ + if (unshare(CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET) != 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 && !se->exited); + + /* We were terminated by a signal, see fuse_signals.c */ + if (se->exited) { + exit(0); + } + + if (WIFEXITED(wstatus)) { + exit(WEXITSTATUS(wstatus)); + } + + exit(1); + } + + /* Send us SIGTERM when the parent thread terminates, see prctl(2) */ + prctl(PR_SET_PDEATHSIG, SIGTERM); + + /* + * 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); + } + + /* Now we can get our /proc/self/fd directory file descriptor */ + 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) +/* + * Make the source directory our root so symlinks cannot escape and no other + * files are accessible. Assumes unshare(CLONE_NEWNS) was already called. + */ +static void setup_mounts(const char *source) { int oldroot; int newroot; + 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); + } + + /* This magic is based on lxc's lxc_pivot_root() */ oldroot = open("/", O_DIRECTORY | O_RDONLY | O_CLOEXEC); if (oldroot < 0) { fuse_log(FUSE_LOG_ERR, "open(/): %m\n"); @@ -2009,47 +2083,14 @@ static void setup_pivot_root(const char *source) close(oldroot); } -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); - } -} - -/* - * Make the source directory our root so symlinks cannot escape and no other - * files are accessible. - */ -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); - } - - setup_pivot_root(source); -} - /* * Lock down this process to prevent access to other processes or files outside * source directory. This reduces the impact of arbitrary code execution bugs. */ -static void setup_sandbox(struct lo_data *lo) +static void setup_sandbox(struct lo_data *lo, struct fuse_session *se) { - setup_net_namespace(); - setup_mount_namespace(lo->source); + setup_namespaces(lo, se); + setup_mounts(lo->source); } int main(int argc, char *argv[]) @@ -2173,10 +2214,7 @@ int main(int argc, char *argv[]) fuse_daemonize(opts.foreground); - /* Must be after daemonize to get the right /proc/self/fd */ - setup_proc_self_fd(&lo); - - setup_sandbox(&lo); + setup_sandbox(&lo, se); /* Block until ctrl+c or fusermount -u */ ret = virtio_loop(se); -- 1.8.3.1