Add attach.[ch]: Helper functions for lxc-attach

The following helper functions for lxc-attach are added to a new file
attach.c:
 - lxc_proc_get_context_info: Get cgroup memberships, personality and
   capability bounding set from /proc for a given process.
 - lxc_proc_free_context_info: Free the data structure responsible
 - lxc_attach_proc_to_cgroups: Add the process specified by the pid
   parameter to the cgroups given by the ctx parameter.
 - lxc_attach_drop_privs: Drop capabilities to the capability mask given in
   the ctx parameter.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>

3 files changed, 295 insertions, 1 deletions

diff --git a/src/lxc/Makefile.am b/src/lxc/Makefile.am
index 924cf1d..e695883 100644
--- a/src/lxc/Makefile.am
+++ b/src/lxc/Makefile.am
@@ -12,7 +12,8 @@ pkginclude_HEADERS = \
 		conf.h \
 		list.h \
 		log.h \
-		state.h
+		state.h \
+		attach.h
 
 sodir=$(libdir)
 # use PROGRAMS to avoid complains from automake
@@ -41,6 +42,7 @@ liblxc_so_SOURCES = \
 	list.h \
 	state.c state.h \
 	log.c log.h \
+	attach.c attach.h \
 	\
 	network.c network.h \
         nl.c nl.h \
diff --git a/src/lxc/attach.c b/src/lxc/attach.c
new file mode 100644
index 0000000..254b185
--- /dev/null
+++ b/src/lxc/attach.c
@@ -0,0 +1,245 @@
+/*
+ * lxc: linux Container library
+ *
+ * (C) Copyright IBM Corp. 2007, 2008
+ *
+ * Authors:
+ * Daniel Lezcano <dlezcano at fr.ibm.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/param.h>
+#include <sys/prctl.h>
+
+#if !HAVE_DECL_PR_CAPBSET_DROP
+#define PR_CAPBSET_DROP 24
+#endif
+
+#include "namespace.h"
+#include "log.h"
+#include "attach.h"
+#include "caps.h"
+#include "cgroup.h"
+#include "config.h"
+
+#include "setns.h"
+
+lxc_log_define(lxc_attach, lxc);
+
+int setns(int fd, int nstype)
+{
+#ifndef __NR_setns
+	errno = ENOSYS;
+	return -1;
+#else
+	return syscall(__NR_setns, fd, nstype);
+#endif
+}
+
+struct lxc_proc_context_info *lxc_proc_get_context_info(pid_t pid)
+{
+	struct lxc_proc_context_info *info = calloc(1, sizeof(*info));
+	FILE *proc_file;
+	char proc_fn[MAXPATHLEN];
+	char *line = NULL, *ptr, *ptr2;
+	size_t line_bufsz = 0;
+	int ret, found, l;
+	int i;
+
+	if (!info) {
+		SYSERROR("Could not allocate memory.");
+		return NULL;
+	}
+
+	/* read capabilities */
+	snprintf(proc_fn, MAXPATHLEN, "/proc/%d/status", pid);
+
+	proc_file = fopen(proc_fn, "r");
+	if (!proc_file) {
+		SYSERROR("Could not open %s", proc_fn);
+		goto out_error;
+	}
+
+	found = 0;
+	while (getline(&line, &line_bufsz, proc_file) != -1) {
+		ret = sscanf(line, "CapBnd: %llx", &info->capability_mask);
+		if (ret != EOF && ret > 0) {
+			found = 1;
+			break;
+		}
+	}
+
+	fclose(proc_file);
+
+	if (!found) {
+		SYSERROR("Could not read capability bounding set from %s", proc_fn);
+		errno = ENOENT;
+		goto out_error;
+	}
+
+	/* read personality */
+	snprintf(proc_fn, MAXPATHLEN, "/proc/%d/personality", pid);
+
+	proc_file = fopen(proc_fn, "r");
+	if (!proc_file) {
+		SYSERROR("Could not open %s", proc_fn);
+		goto out_error;
+	}
+
+	ret = fscanf(proc_file, "%lx", &info->personality);
+	fclose(proc_file);
+
+	if (ret == EOF || ret == 0) {
+		SYSERROR("Could not read personality from %s", proc_fn);
+		errno = ENOENT;
+		goto out_error;
+	}
+
+	/* read cgroups */
+	snprintf(proc_fn, MAXPATHLEN, "/proc/%d/cgroup", pid);
+
+	proc_file = fopen(proc_fn, "r");
+	if (!proc_file) {
+		SYSERROR("Could not open %s", proc_fn);
+		goto out_error;
+	}
+
+	/* we don't really know how many cgroup subsystems there are
+	 * mounted, so we go through the whole file twice */
+	i = 0;
+	while (getline(&line, &line_bufsz, proc_file) != -1) {
+		/* we assume that all lines containing at least two colons
+		 * are valid */
+		ptr = strchr(line, ':');
+		if (ptr && strchr(ptr + 1, ':'))
+			i++;
+	}
+
+	rewind(proc_file);
+
+	info->cgroups = calloc(i, sizeof(*(info->cgroups)));
+	info->cgroups_count = i;
+
+	i = 0;
+	while (getline(&line, &line_bufsz, proc_file) != -1 && i < info->cgroups_count) {
+		/* format of the lines is:
+		 * id:subsystems:path, where subsystems are separated by
+		 * commas and each subsystem may also be of the form
+		 * name=xxx if it describes a private named hierarchy
+		 * we will ignore the id in the following */
+		ptr = strchr(line, ':');
+		ptr2 = ptr ? strchr(ptr + 1, ':') : NULL;
+
+		/* ignore invalid lines */
+		if (!ptr || !ptr2) continue;
+
+		l = strlen(ptr2) - 1;
+		if (ptr2[l] == '\n')
+			ptr2[l] = '\0';
+
+		info->cgroups[i].subsystems = strndup(ptr + 1, ptr2 - (ptr + 1));
+		info->cgroups[i].cgroup = strdup(ptr2 + 1);
+
+		i++;
+	}
+
+	free(line);
+	fclose(proc_file);
+
+	return info;
+
+out_error:
+	lxc_proc_free_context_info(info);
+	free(line);
+	return NULL;
+}
+
+void lxc_proc_free_context_info(struct lxc_proc_context_info *info)
+{
+	if (!info)
+		return;
+
+	if (info->cgroups) {
+		int i;
+		for (i = 0; i < info->cgroups_count; i++) {
+			free(info->cgroups[i].subsystems);
+			free(info->cgroups[i].cgroup);
+		}
+	}
+	free(info->cgroups);
+	free(info);
+}
+
+int lxc_attach_proc_to_cgroups(pid_t pid, struct lxc_proc_context_info *ctx)
+{
+	int i, ret;
+
+	if (!ctx) {
+		ERROR("No valid context supplied when asked to attach "
+		      "process to cgroups.");
+		return -1;
+	}
+
+	for (i = 0; i < ctx->cgroups_count; i++) {
+		char *path;
+
+		/* the kernel should return paths that start with '/' */
+		if (ctx->cgroups[i].cgroup[0] != '/') {
+			ERROR("For cgroup subsystem(s) %s the path '%s' does "
+			      "not start with a '/'",
+			      ctx->cgroups[i].subsystems,
+			      ctx->cgroups[i].cgroup);
+			return -1;
+		}
+
+		/* lxc_cgroup_path_get can process multiple subsystems */
+		ret = lxc_cgroup_path_get(&path, ctx->cgroups[i].subsystems,
+		                          &ctx->cgroups[i].cgroup[1]);
+		if (ret)
+			return -1;
+
+		ret = lxc_cgroup_attach(path, pid);
+		if (ret)
+			return -1;
+	}
+
+	return 0;
+}
+
+int lxc_attach_drop_privs(struct lxc_proc_context_info *ctx)
+{
+	int last_cap = lxc_caps_last_cap();
+	int cap;
+
+	for (cap = 0; cap <= last_cap; cap++) {
+		if (ctx->capability_mask & (1LL << cap))
+			continue;
+
+		if (prctl(PR_CAPBSET_DROP, cap, 0, 0, 0)) {
+			SYSERROR("failed to remove capability id %d", cap);
+			return -1;
+		}
+	}
+
+	return 0;
+}
diff --git a/src/lxc/attach.h b/src/lxc/attach.h
new file mode 100644
index 0000000..7e67455
--- /dev/null
+++ b/src/lxc/attach.h
@@ -0,0 +1,47 @@
+/*
+ * lxc: linux Container library
+ *
+ * (C) Copyright IBM Corp. 2007, 2008
+ *
+ * Authors:
+ * Daniel Lezcano <dlezcano at fr.ibm.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef _attach_h
+#define _attach_h
+
+#include <sys/types.h>
+
+struct lxc_proc_cgroup_info {
+	char *subsystems;
+	char *cgroup;
+};
+
+struct lxc_proc_context_info {
+	unsigned long personality;
+	unsigned long long capability_mask;
+	struct lxc_proc_cgroup_info* cgroups;
+	int cgroups_count;
+};
+
+extern struct lxc_proc_context_info *lxc_proc_get_context_info(pid_t pid);
+extern void lxc_proc_free_context_info(struct lxc_proc_context_info *info);
+
+extern int lxc_attach_proc_to_cgroups(pid_t pid, struct lxc_proc_context_info *ctx);
+extern int lxc_attach_drop_privs(struct lxc_proc_context_info *ctx);
+
+#endif