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 <mszeredi@redhat.com> Message-Id: <20200429124733.22488-1-mszeredi@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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@ -2536,6 +2536,8 @@ static void print_capabilities(void)
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static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
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static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
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{
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{
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pid_t child;
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pid_t child;
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char template[] = "virtiofsd-XXXXXX";
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char *tmpdir;
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/*
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/*
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* Create a new pid namespace for *child* processes. We'll have to
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* Create a new pid namespace for *child* processes. We'll have to
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@ -2597,12 +2599,33 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
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exit(1);
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exit(1);
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}
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}
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/* Now we can get our /proc/self/fd directory file descriptor */
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tmpdir = mkdtemp(template);
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lo->proc_self_fd = open("/proc/self/fd", O_PATH);
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if (!tmpdir) {
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if (lo->proc_self_fd == -1) {
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fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template);
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fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
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exit(1);
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exit(1);
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}
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}
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if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) {
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fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n",
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tmpdir);
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exit(1);
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}
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/* Now we can get our /proc/self/fd directory file descriptor */
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lo->proc_self_fd = open(tmpdir, O_PATH);
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if (lo->proc_self_fd == -1) {
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fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir);
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exit(1);
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}
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if (umount2(tmpdir, MNT_DETACH) < 0) {
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fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir);
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exit(1);
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}
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if (rmdir(tmpdir) < 0) {
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fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir);
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}
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}
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}
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/*
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/*
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