linux-kernel - [PATCH v3 2/4] vfs,userns: Ensure real root is always capable towards inodes

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Message-Id: <1410532905-114262-3-git-send-email-seth.forshee@canonical.com>
Date:	Fri, 12 Sep 2014 09:41:43 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Miklos Szeredi <miklos@...redi.hu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Serge Hallyn <serge.hallyn@...ntu.com>,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Seth Forshee <seth.forshee@...onical.com>
Subject: [PATCH v3 2/4] vfs,userns: Ensure real root is always capable towards inodes

Currently root is restricted from performing some modifications
to inodes whose owner is INVALID_UID or group is INVALID_GID
because this id doesn't map into any user namespace. Add a
special case to the relevant checks to make sure root is always
capable of performing these operations.

Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
---
 fs/inode.c          | 3 +++
 kernel/capability.c | 6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 26753ba7b6d6..1029320ff029 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1840,6 +1840,9 @@ bool inode_owner_or_capable(const struct inode *inode)
 {
 	struct user_namespace *ns;
 
+	if (capable(CAP_SYS_ADMIN))
+		return true;
+
 	if (uid_eq(current_fsuid(), inode->i_uid))
 		return true;
 
diff --git a/kernel/capability.c b/kernel/capability.c
index 989f5bfc57dc..a472eaa52b6a 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -438,8 +438,12 @@ EXPORT_SYMBOL(capable);
  */
 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 {
-	struct user_namespace *ns = current_user_ns();
+	struct user_namespace *ns;
 
+	if (capable(CAP_SYS_ADMIN))
+		return true;
+
+	ns = current_user_ns();
 	return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
 		kgid_has_mapping(ns, inode->i_gid);
 }
-- 
1.9.1

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