From d59766a64806d3acc409bd27cdd6a58e2d6e405f Mon Sep 17 00:00:00 2001
From: Vaclav Dolezal <vdolezal@redhat.com>
Date: Fri, 20 Apr 2018 17:57:39 +0200
Subject: [PATCH] mount: allow PID as --namespace argument

[[kzak@redhat.com: - update code]

Signed-off-by: Karel Zak <kzak@redhat.com>
Signed-off-by: Vaclav Dolezal <vdolezal@redhat.com>
---
 sys-utils/mount.8 |  4 +++-
 sys-utils/mount.c | 25 +++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/sys-utils/mount.8 b/sys-utils/mount.8
index 488403717..1a05f71c0 100644
--- a/sys-utils/mount.8
+++ b/sys-utils/mount.8
@@ -646,7 +646,9 @@ is on a read-only filesystem.
 .TP
 .BR \-N , " \-\-namespace " \fIns
 Perform mount in namespace specified by \fIns\fR.
-\fIns\fR is typically in form \fI/proc/[pid]/ns/mnt\fR.
+\fIns\fR is either PID of process running in that namespace
+or special file representing that namespace.
+See \fBnamespaces\fR(7) for more information.
 .TP
 .BR \-O , " \-\-test\-opts " \fIopts
 Limit the set of filesystems to which the
diff --git a/sys-utils/mount.c b/sys-utils/mount.c
index a0dba721a..5e139e896 100644
--- a/sys-utils/mount.c
+++ b/sys-utils/mount.c
@@ -512,6 +512,19 @@ static long osrc2mask(const char *str, size_t len)
 	return -EINVAL;
 }
 
+static pid_t parse_pid(const char *str)
+{
+	char *end;
+	pid_t ret;
+
+	errno = 0;
+	ret = strtoul(str, &end, 10);
+
+	if (ret < 0 || errno || end == str || (end && *end))
+		return 0;
+	return ret;
+}
+
 int main(int argc, char **argv)
 {
 	int c, rc = MNT_EX_SUCCESS, all = 0, show_labels = 0;
@@ -694,9 +707,17 @@ int main(int argc, char **argv)
 			append_option(cxt, "rbind");
 			break;
 		case 'N':
-			if (mnt_context_set_target_ns(cxt, optarg))
-				err(MNT_EX_SYSERR, _("failed to set target namespace"));
+		{
+			char path[PATH_MAX];
+			pid_t pid = parse_pid(optarg);
+
+			if (pid)
+				snprintf(path, sizeof(path), "/proc/%i/ns/mnt", pid);
+
+			if (mnt_context_set_target_ns(cxt, pid ? path : optarg))
+				err(MNT_EX_SYSERR, _("failed to set target namespace to %s"), pid ? path : optarg);
 			break;
+		}
 		case MOUNT_OPT_SHARED:
 			append_option(cxt, "shared");
 			propa = 1;