From fd9279ec9985d9c8a0b533eff24839f93695b0f4 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Mon, 27 Jul 2020 20:02:23 +0100 Subject: [PATCH] virtiofsd: probe unshare(CLONE_FS) and print an error An assertion failure is raised during request processing if unshare(CLONE_FS) fails. Implement a probe at startup so the problem can be detected right away. Unfortunately Docker/Moby does not include unshare in the seccomp.json list unless CAP_SYS_ADMIN is given. Other seccomp.json lists always include unshare (e.g. podman is unaffected): https://raw.githubusercontent.com/seccomp/containers-golang/master/seccomp.json Use "docker run --security-opt seccomp=path/to/seccomp.json ..." if the default seccomp.json is missing unshare. Cc: Misono Tomohiro Signed-off-by: Stefan Hajnoczi Message-Id: <20200727190223.422280-4-stefanha@redhat.com> Reviewed-by: Misono Tomohiro Signed-off-by: Dr. David Alan Gilbert --- tools/virtiofsd/fuse_virtio.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c index 3b6d16a041..9e5537506c 100644 --- a/tools/virtiofsd/fuse_virtio.c +++ b/tools/virtiofsd/fuse_virtio.c @@ -949,6 +949,22 @@ int virtio_session_mount(struct fuse_session *se) { int ret; + /* + * Test that unshare(CLONE_FS) works. fv_queue_worker() will need it. It's + * an unprivileged system call but some Docker/Moby versions are known to + * reject it via seccomp when CAP_SYS_ADMIN is not given. + * + * Note that the program is single-threaded here so this syscall has no + * visible effect and is safe to make. + */ + ret = unshare(CLONE_FS); + if (ret == -1 && errno == EPERM) { + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_FS) failed with EPERM. If " + "running in a container please check that the container " + "runtime seccomp policy allows unshare.\n"); + return -1; + } + ret = fv_create_listen_socket(se); if (ret < 0) { return ret;