From: Fabian Vogt <fvogt@suse.de>
Date: Wed, 1 Apr 2020 11:15:13 +0000 (+0200)
Subject: libmount: Avoid triggering autofs in lookup_umount_fs_by_statfs
X-Git-Tag: v2.36-rc1~152
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=7065cc0e5312cafc5ae3e4c342f78f264300fb5f;p=thirdparty%2Futil-linux.git

libmount: Avoid triggering autofs in lookup_umount_fs_by_statfs

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.
---

diff --git a/libmount/src/context_umount.c b/libmount/src/context_umount.c
index 733e9194db..e3547d3564 100644
--- a/libmount/src/context_umount.c
+++ b/libmount/src/context_umount.c
@@ -287,9 +287,13 @@ static int lookup_umount_fs_by_statfs(struct libmnt_context *cxt, const char *tg
 	if (!type) {
 		struct statfs vfs;
 
-		DBG(CXT, ul_debugobj(cxt, "  trying statfs()"));
-		if (statfs(tgt, &vfs) == 0)
+		DBG(CXT, ul_debugobj(cxt, "  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) {
 			int rc = mnt_fs_set_fstype(cxt->fs, type);
 			if (rc)