mntns: crtools: stat pathes relatively of a mntns root

If we dump tasks with mntns, we should look at pathes from point of a mntns root.

Now we support a situation when a root of an init task has the same root as the
mntns root, because we have not another way to get a root of mntns.

A path to an unix socket is copied, because the origin copy will be gone
out from the function, where it was created.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -45,6 +45,7 @@
 #include "eventpoll.h"
 #include "inotify.h"
 #include "pstree.h"
+#include "mount.h"
 
 #include "protobuf.h"
 #include "protobuf/fdinfo.pb-c.h"
@@ -1474,6 +1475,9 @@ int cr_dump_tasks(pid_t pid, const struct cr_options *opts)
 	 * in the dump stage
 	 */
 
+	if (mntns_collect_root(root_item->pid.real))
+		goto err;
+
 	collect_sockets();
 
 	glob_fdset = cr_glob_fdset_open(O_DUMP);

files-reg.c

@@ -7,6 +7,7 @@
 
 #include "crtools.h"
 
+#include "mount.h"
 #include "files.h"
 #include "image.h"
 #include "list.h"
@@ -257,7 +258,7 @@ dump_entry:
 			&rpe, remap_file_path_entry);
 }
 
-static int check_path_remap(char *path, const struct stat *ost, int lfd, u32 id)
+static int check_path_remap(char *rpath, const struct stat *ost, int lfd, u32 id)
 {
 	int ret;
 	struct stat pst;
@@ -269,9 +270,9 @@ static int check_path_remap(char *path, const struct stat *ost, int lfd, u32 id)
 		 * be careful whether anybody still has any of its hardlinks
 		 * also open.
 		 */
-		return dump_ghost_remap(path, ost, lfd, id);
+		return dump_ghost_remap(rpath + 1, ost, lfd, id);
 
-	ret = stat(path, &pst);
+	ret = fstatat(mntns_root, rpath, &pst, 0);
 	if (ret < 0) {
 		/*
 		 * FIXME linked file, but path is not accessible (unless any
@@ -304,13 +305,13 @@ static int check_path_remap(char *path, const struct stat *ost, int lfd, u32 id)
 int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
 {
 	char fd_str[128];
-	char path[PATH_MAX];
+	char rpath[PATH_MAX + 1] = ".", *path = rpath + 1;;
 	int len, rfd;
 
 	RegFileEntry rfe = REG_FILE_ENTRY__INIT;
 
 	snprintf(fd_str, sizeof(fd_str), "/proc/self/fd/%d", lfd);
-	len = readlink(fd_str, path, sizeof(path) - 1);
+	len = readlink(fd_str, path, sizeof(rpath) - 2);
 	if (len < 0) {
 		pr_perror("Can't readlink %s", fd_str);
 		return len;
@@ -320,7 +321,7 @@ int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
 	pr_info("Dumping path for %d fd via self %d [%s]\n",
 			p->fd, lfd, path);
 
-	if (check_path_remap(path, &p->stat, lfd, id))
+	if (check_path_remap(rpath, &p->stat, lfd, id))
 		return -1;
 
 	rfe.id		= id;

include/mount.h

 #ifndef MOUNT_H__
 #define MOUNT_H__
 
+extern int mntns_root;
+int mntns_collect_root(pid_t pid);
+
 struct proc_mountinfo;
 
 extern int open_mount(unsigned int s_dev);

mount.c

@@ -22,6 +22,7 @@
 #include "protobuf/mnt.pb-c.h"
 
 static struct mount_info *mntinfo;
+int mntns_root = -1;
 
 int open_mount(unsigned int s_dev)
 {
@@ -499,3 +500,37 @@ void show_mountpoints(int fd, struct cr_options *o)
 {
 	pb_show_plain(fd, mnt_entry);
 }
+
+int mntns_collect_root(pid_t pid)
+{
+	int fd, pfd;
+	int ret;
+	char path[PATH_MAX + 1];
+
+	/* If /proc/pid/root links on '/', it signs that a root of the task
+	 * and a root of mntns is the same. */
+
+	pfd = open_pid_proc(pid);
+	ret = readlinkat(pfd, "root", path, PATH_MAX);
+	if (ret < 0)
+		return ret;
+
+	path[ret + 1] = '\0';
+
+	if (ret != 1 || path[0] != '/') {
+		pr_err("The root task has another root than mntns: %s\n", path);
+		close_pid_proc();
+		return -1;
+	}
+
+	fd = openat(pfd, "root", O_RDONLY | O_DIRECTORY, 0);
+	close_pid_proc();
+	if (fd < 0) {
+		pr_perror("Can't open the task root");
+		return -1;
+	}
+
+	mntns_root = fd;
+
+	return 0;
+}

sk-unix.c

@@ -19,6 +19,7 @@
 #include "util-net.h"
 #include "sockets.h"
 #include "sk-queue.h"
+#include "mount.h"
 
 #include "protobuf.h"
 #include "protobuf/sk-unix.pb-c.h"
@@ -261,6 +262,7 @@ static int unix_collect_one(const struct unix_diag_msg *m,
 		if (name[0] != '\0') {
 			struct unix_diag_vfs *uv;
 			struct stat st;
+			char rpath[PATH_MAX];
 
 			if (name[0] != '/') {
 				pr_warn("Relative bind path '%s' "
@@ -275,9 +277,10 @@ static int unix_collect_one(const struct unix_diag_msg *m,
 			}
 
 			uv = RTA_DATA(tb[UNIX_DIAG_VFS]);
-			if (stat(name, &st)) {
+			snprintf(rpath, sizeof(rpath), ".%s", name);
+			if (fstatat(mntns_root, rpath, &st, 0)) {
 				pr_perror("Can't stat socket %d(%s)",
-						m->udiag_ino, name);
+						m->udiag_ino, rpath);
 				goto skip;
 			}