[lxc-devel] [PATCH v2 7/7] added the unmount-namespace hook

[Wolfgang Bumiller]

Signed-off-by: Wolfgang Bumiller <w.bumiller at proxmox.com>
---
 hooks/Makefile.am         |   6 ++
 hooks/unmount-namespace.c | 180 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 186 insertions(+)
 create mode 100644 hooks/unmount-namespace.c

diff --git a/hooks/Makefile.am b/hooks/Makefile.am
index be55601..ef82083 100644
--- a/hooks/Makefile.am
+++ b/hooks/Makefile.am
@@ -6,4 +6,10 @@ hooks_SCRIPTS = \
 	ubuntu-cloud-prep \
 	squid-deb-proxy-client
 
+hooks_PROGRAMS = \
+	unmount-namespace
+
+unmount_namespace_SOURCES = \
+	unmount-namespace.c
+
 EXTRA_DIST=$(hooks_SCRIPTS)
diff --git a/hooks/unmount-namespace.c b/hooks/unmount-namespace.c
new file mode 100644
index 0000000..aa64985
--- /dev/null
+++ b/hooks/unmount-namespace.c
@@ -0,0 +1,180 @@
+/*
+ * Copyright © 2015 Wolfgang Bumiller <w.bumiller at proxmox.com>.
+ * Copyright © 2015 Proxmox Server Solutions GmbH
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#define _GNU_SOURCE    /* setns */
+#include <stdio.h>     /* fdopen, getmntent, endmntent */
+#include <stdlib.h>    /* malloc, qsort */
+#include <unistd.h>    /* close */
+#include <string.h>    /* strcmp, strncmp, strdup, strerror */
+#include <sched.h>     /* setns */
+#include <sys/mount.h> /* umount2 */
+#include <sys/types.h> /* openat, open */
+#include <sys/stat.h>  /* openat, open */
+#include <fcntl.h>     /* openat, open */
+#include <mntent.h>    /* getmntent, endmntent */
+#include <errno.h>     /* errno */
+
+struct mount {
+	char *src; /* currently not used */
+	char *dst;
+	char *fs; /* currently not used */
+};
+
+static void mount_free(struct mount *mnt) {
+	free(mnt->src);
+	free(mnt->dst);
+	free(mnt->fs);
+}
+
+static int mount_cmp_dst(const void *a_, const void *b_) {
+	struct mount *a = (struct mount*)a_;
+	struct mount *b = (struct mount*)b_;
+	return strcmp(b->dst, a->dst); /* swapped order */
+}
+
+/* Unmounting /dev/pts fails, and  so /dev also fails, but /dev is not what
+ * we're interested in.
+ */
+static int mount_should_error(const struct mount *mnt) {
+	const char *dst = mnt->dst;
+	return !(strncmp(dst, "/dev", 4) == 0 && (dst[4] == 0 || dst[4] == '/'));
+}
+
+/* Read mounts from 'self/mounts' relative to a directory filedescriptor.
+ * Before entering the container we open a handle to /proc on the host as we
+ * need to access /proc/self/mounts and the container's /proc doesn't contain
+ * our /self. We then use openat(2) to avoid having to mount a temporary /proc.
+ */
+static int read_mounts(int procfd, struct mount **mp, size_t *countp) {
+	int fd;
+	struct mntent *ent;
+	FILE *mf;
+	size_t capacity = 32;
+	size_t count = 0;
+	struct mount *mounts = (struct mount*)malloc(capacity * sizeof(*mounts));
+
+	*mp = NULL;
+	*countp = 0;
+
+	fd = openat(procfd, "self/mounts", O_RDONLY);
+	if (fd < 0)
+		return 0;
+
+	mf = fdopen(fd, "r");
+	if (!mf) {
+		int error = errno;
+		close(fd);
+		errno = error;
+		return 0;
+	}
+	while ((ent = getmntent(mf))) {
+		if (count == capacity) {
+			capacity *= 2;
+			mounts = (struct mount*)realloc(mounts, capacity * sizeof(*mounts));
+		}
+		mounts[count].src = strdup(ent->mnt_fsname);
+		mounts[count].dst = strdup(ent->mnt_dir);
+		mounts[count].fs  = strdup(ent->mnt_type);
+		++count;
+	}
+	endmntent(mf);
+
+	*mp = mounts;
+	*countp = count;
+
+	return 1;
+}
+
+int main(int argc, char **argv) {
+	int i, procfd, ctmntfd;
+	struct mount *mounts;
+	size_t zi, count = 0;
+	const char *mntns = NULL;
+
+	if (argc < 4 || strcmp(argv[2], "lxc") != 0) {
+		fprintf(stderr, "%s: usage error, expected LXC hook arguments\n", argv[0]);
+		return 2;
+	}
+
+	if (strcmp(argv[3], "stop") != 0)
+		return 0;
+
+	for (i = 4; i != argc; ++i) {
+		if (!strncmp(argv[i], "mnt:", 4))
+			mntns = argv[i] + 4;
+	}
+
+	if (!mntns) {
+		fprintf(stderr, "%s: no mount namespace provided\n", argv[0]);
+		return 3;
+	}
+
+	/* Open a handle to /proc on the host as we need to access /proc/self/mounts
+	 * and the container's /proc doesn't contain our /self. See read_mounts().
+	 */
+	procfd = open("/proc", O_RDONLY | O_DIRECTORY | O_PATH);
+	if (procfd < 0) {
+		fprintf(stderr, "%s: failed to open /proc: %s\n", argv[0], strerror(errno));
+		return 4;
+	}
+
+	/* Open the mount namespace and enter it. */
+	ctmntfd = open(mntns, O_RDONLY);
+	if (ctmntfd < 0) {
+		fprintf(stderr, "%s: failed to open mount namespace: %s\n",
+			argv[0], strerror(errno));
+		close(procfd);
+		return 5;
+	}
+
+	if (setns(ctmntfd, CLONE_NEWNS) != 0) {
+		fprintf(stderr, "%s: failed to attach to namespace: %s\n",
+			argv[0], strerror(errno));
+		close(ctmntfd);
+		close(procfd);
+		return 6;
+	}
+	close(ctmntfd);
+
+	/* Now read [[procfd]]/self/mounts */
+	if (!read_mounts(procfd, &mounts, &count)) {
+		fprintf(stderr, "%s: failed to read mountpoints: %s\n",
+			argv[0], strerror(errno));
+		close(procfd);
+		return 7;
+	}
+	close(procfd);
+
+	/* Just sort to get a sane unmount-order... */
+	qsort(mounts, count, sizeof(*mounts), &mount_cmp_dst);
+
+	for (zi = 0; zi != count; ++zi) {
+		/* fprintf(stderr, "Unmount: %s\n", mounts[zi].dst); */
+		if (umount2(mounts[zi].dst, 0) != 0) {
+			int error = errno;
+			if (mount_should_error(&mounts[zi])) {
+				fprintf(stderr, "%s: failed to unmount %s: %s\n",
+					argv[0], mounts[zi].dst, strerror(error));
+			}
+		}
+		mount_free(&mounts[zi]);
+	}
+	free(mounts);
+
+	return 0;
+}
-- 
2.1.4