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Subject[PATCH 1/1] overlayfs: apply device cgroup and security permissions to overlay files
Date
When checking permissions on an overlayfs inode we do not take into
account either device cgroup restrictions nor security permissions.
This allows a user to mount an overlayfs layer over a restricted device
directory and by pass those permissions to open otherwise restricted
files.

Use devcgroup_inode_permission() and security_inode_permission() against
the underlying inodes when calculating ovl_permission().

Signed-off-by: Andy Whitcroft <apw@canonical.com>
---
fs/overlayfs/inode.c | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)

Not sure whether you saw this the first time round. This was shown
up in testing with containers, specifically with device cgroups.
It seems we should be re-checking here else users can simply
bypass the containers device permissions by mounting an overlayfs
fs over them.

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index ba1a777..1145a76 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -10,6 +10,8 @@
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/xattr.h>
+#include <linux/device_cgroup.h>
+#include <linux/security.h>
#include "overlayfs.h"

int ovl_setattr(struct dentry *dentry, struct iattr *attr)
@@ -118,6 +120,11 @@ int ovl_permission(struct inode *inode, int mask)
err = realinode->i_op->permission(realinode, mask);
else
err = generic_permission(realinode, mask);
+
+ if (!err)
+ err = devcgroup_inode_permission(realinode, mask);
+ if (!err)
+ err = security_inode_permission(realinode, mask);
out_dput:
dput(alias);
return err;
--
1.7.9


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