parasite: get a file descriptor for procfs from a target pidns (v2)

It will be used for dumping zombies.

v2: Add a fast path, if /proc belongs to the target pipns. it's usually for CT.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/parasite-syscall.h

@@ -42,6 +42,7 @@ struct fd_opts;
 extern int parasite_drain_fds_seized(struct parasite_ctl *ctl,
 					struct parasite_drain_fd *dfds,
 					int *lfds, struct fd_opts *flags);
+extern int parasite_get_proc_fd_seized(struct parasite_ctl *ctl);
 
 extern int parasite_cure_seized(struct parasite_ctl *ctl);
 extern struct parasite_ctl *parasite_infect_seized(pid_t pid,

include/parasite.h

@@ -31,6 +31,7 @@ enum {
 	PARASITE_CMD_DUMP_MISC,
 	PARASITE_CMD_DUMP_TID_ADDR,
 	PARASITE_CMD_DRAIN_FDS,
+	PARASITE_CMD_GET_PROC_FD,
 
 	PARASITE_CMD_MAX,
 };

include/syscall-x86-64.def

@@ -40,7 +40,10 @@ __NR_wait4		61		sys_waitpid		(int pid, int *status, int options, struct rusage *
 __NR_kill		62		sys_kill		(long pid, int sig)
 __NR_fcntl		72		sys_fcntl		(int fd, int type, long arg)
 __NR_flock		73		sys_flock		(int fd, unsigned long cmd)
+__NR_mkdir		83		sys_mkdir		(const char *name, int mode)
+__NR_rmdir		84		sys_rmdir		(const char *name)
 __NR_unlink		87		sys_unlink		(char *pathname)
+__NR_readlink		89		sys_readlink		(const char *path, char *buf, int bufsize)
 __NR_setresuid		117		sys_setresuid		(int uid, int euid, int suid)
 __NR_setresgid		119		sys_setresgid		(int gid, int egid, int sgid)
 __NR_getpgid		121		sys_getpgid		(void)
@@ -51,6 +54,8 @@ __NR_capset		126		sys_capset		(struct cap_header *h, struct cap_data *d)
 __NR_personality	135		sys_personality		(unsigned int personality)
 __NR_prctl		157		sys_prctl		(int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5)
 __NR_arch_prctl		158		sys_arch_prctl		(int option, unsigned long addr)
+__NR_mount		165		sys_mount		(char *dev_nmae, char *dir_name, char *type, unsigned long flags, void *data)
+__NR_umount2		166		sys_umount2		(char *name, int flags)
 __NR_gettid		186		sys_gettid		(void)
 __NR_futex		202		sys_futex		(u32 *uaddr, int op, u32 val, struct timespec *utime, u32 *uaddr2, u32 val3)
 __NR_set_thread_area	205		sys_set_thread_area	(user_desc_t *info)

parasite-syscall.c

@@ -623,6 +623,25 @@ err:
 	return ret;
 }
 
+int parasite_get_proc_fd_seized(struct parasite_ctl *ctl)
+{
+	int ret = -1, fd;
+
+	ret = parasite_execute(PARASITE_CMD_GET_PROC_FD, ctl, NULL, 0);
+	if (ret) {
+		pr_err("Parasite failed to get proc fd\n");
+		return ret;
+	}
+
+	fd = recv_fd(ctl->tsock);
+	if (fd < 0) {
+		pr_err("Can't retrieve FD from socket\n");
+		return fd;
+	}
+
+	return fd;
+}
+
 int parasite_cure_seized(struct parasite_ctl *ctl)
 {
 	int ret = 0;

parasite.c

 #include <sys/mman.h>
 #include <errno.h>
 #include <signal.h>
+#include <linux/limits.h>
+#include <sys/mount.h>
 
 #include "syscall.h"
 #include "parasite.h"
@@ -375,6 +377,58 @@ static int init(struct parasite_init_args *args)
 	return ret;
 }
 
+static char proc_mountpoint[] = "proc.crtools";
+static int parasite_get_proc_fd()
+{
+	int ret, fd;
+	char buf[2];
+
+	ret = sys_readlink("/proc/self", buf, sizeof(buf));
+	if (ret < 0 && ret != -ENOENT) {
+		sys_write_msg("Can't readlink /proc/self\n");
+		return ret;
+	}
+
+	/* Fast path -- if /proc belongs to this pidns */
+	if (ret == 1 && buf[0] == '1') {
+		fd = sys_open("/proc", O_RDONLY, 0);
+		goto out_send_fd;
+	}
+
+	if (sys_mkdir(proc_mountpoint, 0700)) {
+		sys_write_msg("Can't create a directory ");
+		sys_write_msg(proc_mountpoint);
+		sys_write_msg("\n");
+		return ret;
+	}
+
+	if (sys_mount("proc", proc_mountpoint, "proc", MS_MGC_VAL, NULL)) {
+		sys_write_msg("mount failed\n");
+		ret = -1;
+		goto out_rmdir;
+	}
+
+	fd = sys_open(proc_mountpoint, O_RDONLY, 0);
+
+	if (sys_umount2(proc_mountpoint, MNT_DETACH)) {
+		sys_write_msg("Can't umount procfs\n");
+		return -1;
+	}
+
+out_rmdir:
+	if (sys_rmdir(proc_mountpoint)) {
+		sys_write_msg("Can't remove directory\n");
+		return -1;
+	}
+
+out_send_fd:
+	if (fd < 0)
+		return fd;
+	ret = send_fd(tsock, NULL, 0, fd);
+	sys_close(fd);
+	return ret;
+}
+
 static int parasite_set_logfd()
 {
 	int ret;
@@ -430,6 +484,8 @@ int __used parasite_service(unsigned long cmd, void *args)
 		return dump_tid_info((struct parasite_dump_tid_info *)args);
 	case PARASITE_CMD_DRAIN_FDS:
 		return drain_fds((struct parasite_drain_fd *)args);
+	case PARASITE_CMD_GET_PROC_FD:
+		return parasite_get_proc_fd();
 	}
 
 	sys_write_msg("Unknown command to parasite\n");