linux-kernel - [PATCH 05/16] vfs: Allow unlink, and rename on expirable file mounts

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Date:	Fri, 15 Apr 2016 10:35:21 -0500
From:	"Eric W. Biederman" <ebiederm@...ssion.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>, security@...ian.org,
	security@...nel.org, Al Viro <viro@...iv.linux.org.uk>,
	security@...ntu.com, Peter Hurley <peter@...leysoftware.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Willy Tarreau <w@....eu>,
	Aurelien Jarno <aurelien@...el32.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jann Horn <jann@...jh.net>, Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.com>,
	Florian Weimer <fw@...eb.enyo.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 05/16] vfs: Allow unlink, and rename on expirable file mounts

This is motivated by /dev/ptmx now being an automount.  Given that
automounts eventually will go away I don't see that there is a point
in making unlink and rename to wait until the automounts actually go
away before allowing an operation.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/namespace.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 714778360c2b..278ecb7b8e8e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -718,8 +718,14 @@ bool __is_local_mountpoint(struct dentry *dentry)
 	down_read(&namespace_sem);
 	list_for_each_entry(mnt, &ns->list, mnt_list) {
 		is_covered = (mnt->mnt_mountpoint == dentry);
-		if (is_covered)
+		if (is_covered) {
+			if (!d_is_dir(dentry) &&
+			    (mnt->mnt.mnt_flags & MNT_SHRINKABLE)) {
+				is_covered = false;
+				continue;
+			}
 			break;
+		}
 	}
 	up_read(&namespace_sem);
 out:
-- 
2.8.1