From 397ae982f4df46e7d4b2625c431062c9146f3b83 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Wed, 29 Apr 2020 14:47:33 +0200 Subject: [PATCH] virtiofsd: jail lo->proc_self_fd While it's not possible to escape the proc filesystem through lo->proc_self_fd, it is possible to escape to the root of the proc filesystem itself through "../..". Use a temporary mount for opening lo->proc_self_fd, that has it's root at /proc/self/fd/, preventing access to the ancestor directories. Signed-off-by: Miklos Szeredi Message-Id: <20200429124733.22488-1-mszeredi@redhat.com> Reviewed-by: Stefan Hajnoczi Signed-off-by: Dr. David Alan Gilbert --- tools/virtiofsd/passthrough_ll.c | 31 +++++++++++++++++++++++++++---- 1 file changed, 27 insertions(+), 4 deletions(-) diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index f7b9c1d20c..d7a6474b6e 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -2536,6 +2536,8 @@ static void print_capabilities(void) static void setup_namespaces(struct lo_data *lo, struct fuse_session *se) { pid_t child; + char template[] = "virtiofsd-XXXXXX"; + char *tmpdir; /* * Create a new pid namespace for *child* processes. We'll have to @@ -2597,12 +2599,33 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se) 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"); + tmpdir = mkdtemp(template); + if (!tmpdir) { + fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template); exit(1); } + + if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n", + tmpdir); + exit(1); + } + + /* Now we can get our /proc/self/fd directory file descriptor */ + lo->proc_self_fd = open(tmpdir, O_PATH); + if (lo->proc_self_fd == -1) { + fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir); + exit(1); + } + + if (umount2(tmpdir, MNT_DETACH) < 0) { + fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir); + exit(1); + } + + if (rmdir(tmpdir) < 0) { + fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir); + } } /*