util-linux/libmount-Avoid-triggering-autofs-in-lookup_umount_fs.patch

From 7065cc0e5312cafc5ae3e4c342f78f264300fb5f Mon Sep 17 00:00:00 2001
From: Fabian Vogt <fvogt@suse.de>
Date: Wed, 1 Apr 2020 13:15:13 +0200
Subject: [PATCH 1/4] libmount: Avoid triggering autofs in
 lookup_umount_fs_by_statfs
References: boo#1168389
Upstream: merged (gh#karelzak/util-linux#1002)

Currently, umount /foo results in a statfs("/foo") call, which triggers
autofs. This can create another mountpoint on /foo, which is then unmounted
later instead of the actual /foo at the time umount was called.

This is especially an issue for umount -R /bar, which just fails with
-EBUSY as the accidental mountpoint is never accounted for and so it tries
to umount /bar before /bar/someautofs.

Replace the direct statfs call with open(path, O_PATH) + fstatfs, which sees
the autofs mount directly, without triggering it.
---
 libmount/src/context_umount.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: util-linux-2.34/libmount/src/context_umount.c
===================================================================
--- util-linux-2.34.orig/libmount/src/context_umount.c
+++ util-linux-2.34/libmount/src/context_umount.c
@@ -283,9 +283,13 @@ static int lookup_umount_fs(struct libmn
 		if (!type) {
 			struct statfs vfs;
 
-			DBG(CXT, ul_debugobj(cxt, "umount: trying statfs()"));
-			if (statfs(tgt, &vfs) == 0)
+			DBG(CXT, ul_debugobj(cxt, "umount: trying fstatfs()"));
+			/* O_PATH avoids triggering automount points. */
+			int pathfd = open(tgt, O_PATH);
+			if (pathfd >= 0 && fstatfs(pathfd, &vfs) == 0) {
 				type = mnt_statfs_get_fstype(&vfs);
+				close(pathfd);
+			}
 			if (type) {
 				rc = mnt_fs_set_fstype(cxt->fs, type);
 				if (rc)