linux-kernel - [PATCH 09/24] capability: privileged_wrt_inode

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Date:   Tue, 11 Feb 2020 17:57:38 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Stéphane Graber <stgraber@...ntu.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Aleksa Sarai <cyphar@...har.com>, Jann Horn <jannh@...gle.com>
Cc:     smbarber@...omium.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH 09/24] capability: privileged_wrt_inode_uidgid(): handle fsid mappings

Switch privileged_wrt_inode_uidgid() to lookup fsids in the fsid mappings. If
no fsid mappings are setup the behavior is unchanged, i.e. fsids are looked up
in the id mappings.

Filesystems that share a superblock in all user namespaces they are mounted in
will retain their old semantics even with the introduction of fsidmappings.

Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
 kernel/capability.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/capability.c b/kernel/capability.c
index 1444f3954d75..de7edd5c9900 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -19,6 +19,8 @@
 #include <linux/pid_namespace.h>
 #include <linux/user_namespace.h>
 #include <linux/uaccess.h>
+#include <linux/fsuidgid.h>
+#include <linux/fs.h>
 
 /*
  * Leveraged for setting/resetting capabilities
@@ -484,10 +486,15 @@ EXPORT_SYMBOL(file_ns_capable);
  *
  * Return true if the inode uid and gid are within the namespace.
  */
-bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
+bool privileged_wrt_inode_uidgid(struct user_namespace *ns,
+				 const struct inode *inode)
 {
-	return kuid_has_mapping(ns, inode->i_uid) &&
-		kgid_has_mapping(ns, inode->i_gid);
+	if (is_userns_visible(inode->i_sb->s_iflags))
+		return kuid_has_mapping(ns, inode->i_uid) &&
+		       kgid_has_mapping(ns, inode->i_gid);
+
+	return kfsuid_has_mapping(ns, inode->i_uid) &&
+	       kfsgid_has_mapping(ns, inode->i_gid);
 }
 
 /**
-- 
2.25.0