linux-kernel - [PATCH 3.12 095/124] vfs: Ignore unlocked mounts in fs_fully

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Message-Id: <287bb65a24cc8f3b4b834213cc2145f1b282323c.1438076484.git.jslaby@suse.cz>
Date:	Tue, 28 Jul 2015 11:52:36 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 095/124] vfs: Ignore unlocked mounts in fs_fully_visible

From: "Eric W. Biederman" <ebiederm@...ssion.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit ceeb0e5d39fcdf4dca2c997bf225c7fc49200b37 upstream.

Limit the mounts fs_fully_visible considers to locked mounts.
Unlocked can always be unmounted so considering them adds hassle
but no security benefit.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/namespace.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 9ae6837ef5bf..bdc6223a7500 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2939,11 +2939,15 @@ bool fs_fully_visible(struct file_system_type *type)
 		if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
 			continue;
 
-		/* This mount is not fully visible if there are any child mounts
-		 * that cover anything except for empty directories.
+		/* This mount is not fully visible if there are any
+		 * locked child mounts that cover anything except for
+		 * empty directories.
 		 */
 		list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
 			struct inode *inode = child->mnt_mountpoint->d_inode;
+			/* Only worry about locked mounts */
+			if (!(mnt->mnt.mnt_flags & MNT_LOCKED))
+				continue;
 			if (!S_ISDIR(inode->i_mode))
 				goto next;
 			if (inode->i_nlink > 2)
-- 
2.4.6

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