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Thu, 24 Oct 2019 11:28:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571916515; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ybIvLXARifCanoTHks1af93zgXi2Fkq9toNkp0Uvdtk=; b=NIibLvZ0sbnyhuScirC4qzmybPXDY5qaPfO3ZREG2vkS6o2YTiqUzqZS1/fNwOpkod9mhK j7HdbtbTfHMqFZV8seYPO1Zd8xKj1ubu7iXt5IyguHqxJ1Jjd7G/llOJN3fwDUVcgbYrY5 sMWg8Xbh9IBhOrtmx/0Ic0Zjlx8iiIo= From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, renzhen@linux.alibaba.com, eguan@linux.alibaba.com, ganesh.mahalingam@intel.com, m.mizuma@jp.fujitsu.com, mszeredi@redhat.com, misono.tomohiro@jp.fujitsu.com, tao.peng@linux.alibaba.com, piaojun@huawei.com, stefanha@redhat.com, vgoyal@redhat.com, mst@redhat.com, berrange@redhat.com Subject: [PATCH 16/25] virtiofsd: sandbox mount namespace Date: Thu, 24 Oct 2019 12:27:09 +0100 Message-Id: <20191024112718.34657-17-dgilbert@redhat.com> In-Reply-To: <20191024112718.34657-1-dgilbert@redhat.com> References: <20191024112718.34657-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: uJu0xQ7sN7mrcQGA0fkjGw-1 X-Mimecast-Spam-Score: 0 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @redhat.com) Content-Type: text/plain; charset="utf-8" From: Stefan Hajnoczi Use a mount namespace with the shared directory tree mounted at "/" and no other mounts. This prevents symlink escape attacks because symlink targets are resolved only against the shared directory and cannot go outside it. Signed-off-by: Stefan Hajnoczi Signed-off-by: Peng Tao --- contrib/virtiofsd/passthrough_ll.c | 89 ++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthr= ough_ll.c index 3ddf22d162..20a34d4d83 100644 --- a/contrib/virtiofsd/passthrough_ll.c +++ b/contrib/virtiofsd/passthrough_ll.c @@ -51,6 +51,7 @@ #include #include #include +#include =20 #include "passthrough_helpers.h" =20 @@ -1821,6 +1822,58 @@ static void print_capabilities(void) printf("}\n"); } =20 +/* This magic is based on lxc's lxc_pivot_root() */ +static void setup_pivot_root(const char *source) +{ + int oldroot; + int newroot; + + oldroot =3D open("/", O_DIRECTORY | O_RDONLY | O_CLOEXEC); + if (oldroot < 0) { + fuse_log(FUSE_LOG_ERR, "open(/): %m\n"); + exit(1); + } + + newroot =3D open(source, O_DIRECTORY | O_RDONLY | O_CLOEXEC); + if (newroot < 0) { + fuse_log(FUSE_LOG_ERR, "open(%s): %m\n", source); + exit(1); + } + + if (fchdir(newroot) < 0) { + fuse_log(FUSE_LOG_ERR, "fchdir(newroot): %m\n"); + exit(1); + } + + if (syscall(__NR_pivot_root, ".", ".") < 0){ + fuse_log(FUSE_LOG_ERR, "pivot_root(., .): %m\n"); + exit(1); + } + + if (fchdir(oldroot) < 0) { + fuse_log(FUSE_LOG_ERR, "fchdir(oldroot): %m\n"); + exit(1); + } + + if (mount("", ".", "", MS_SLAVE | MS_REC, NULL) < 0) { + fuse_log(FUSE_LOG_ERR, "mount(., MS_SLAVE | MS_REC): %m\n"); + exit(1); + } + + if (umount2(".", MNT_DETACH) < 0) { + fuse_log(FUSE_LOG_ERR, "umount2(., MNT_DETACH): %m\n"); + exit(1); + } + + if (fchdir(newroot) < 0) { + fuse_log(FUSE_LOG_ERR, "fchdir(newroot): %m\n"); + exit(1); + } + + close(newroot); + close(oldroot); +} + static void setup_proc_self_fd(struct lo_data *lo) { lo->proc_self_fd =3D open("/proc/self/fd", O_PATH); @@ -1830,6 +1883,39 @@ static void setup_proc_self_fd(struct lo_data *lo) } } =20 +/* + * Make the source directory our root so symlinks cannot escape and no oth= er + * files are accessible. + */ +static void setup_mount_namespace(const char *source) +{ + if (unshare(CLONE_NEWNS) !=3D 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 ou= tside + * source directory. This reduces the impact of arbitrary code execution = bugs. + */ +static void setup_sandbox(struct lo_data *lo) +{ + setup_mount_namespace(lo->source); +} + int main(int argc, char *argv[]) { struct fuse_args args =3D FUSE_ARGS_INIT(argc, argv); @@ -1927,6 +2013,7 @@ int main(int argc, char *argv[]) } =20 lo.root.fd =3D open(lo.source, O_PATH); + if (lo.root.fd =3D=3D -1) { fuse_log(FUSE_LOG_ERR, "open(\"%s\", O_PATH): %m\n", lo.source); @@ -1948,6 +2035,8 @@ int main(int argc, char *argv[]) /* Must be after daemonize to get the right /proc/self/fd */ setup_proc_self_fd(&lo); =20 + setup_sandbox(&lo); + /* Block until ctrl+c or fusermount -u */ ret =3D virtio_loop(se); =20 --=20 2.23.0