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From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     =?UTF-8?q?St=C3=A9phane=20Graber?= <stgraber@ubuntu.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Aleksa Sarai <cyphar@cyphar.com>, Jann Horn <jannh@google.com>
Cc:     smbarber@chromium.org, Seth Forshee <seth.forshee@canonical.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Serge Hallyn <serge@hallyn.com>,
        James Morris <jmorris@namei.org>,
        Kees Cook <keescook@chromium.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Phil Estes <estesp@gmail.com>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org,
        containers@lists.linux-foundation.org,
        linux-security-module@vger.kernel.org, linux-api@vger.kernel.org,
        Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH v2 22/28] attr: notify_change(): handle fsid mappings
Date:   Fri, 14 Feb 2020 19:35:48 +0100
Message-Id: <20200214183554.1133805-23-christian.brauner@ubuntu.com>
In-Reply-To: <20200214183554.1133805-1-christian.brauner@ubuntu.com>
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Switch notify_change() 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@ubuntu.com>
---
/* v2 */
unchanged
---
 fs/attr.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index b4bbdbd4c8ca..b3fe9d9582d2 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -17,6 +17,8 @@
 #include <linux/security.h>
 #include <linux/evm.h>
 #include <linux/ima.h>
+#include <linux/fsuidgid.h>
+#include <linux/fs.h>
 
 static bool chown_ok(const struct inode *inode, kuid_t uid)
 {
@@ -310,12 +312,21 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de
 	 * Verify that uid/gid changes are valid in the target
 	 * namespace of the superblock.
 	 */
-	if (ia_valid & ATTR_UID &&
-	    !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
-		return -EOVERFLOW;
-	if (ia_valid & ATTR_GID &&
-	    !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
-		return -EOVERFLOW;
+	if (is_userns_visible(inode->i_sb->s_iflags)) {
+		if (ia_valid & ATTR_UID &&
+		    !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
+			return -EOVERFLOW;
+		if (ia_valid & ATTR_GID &&
+		    !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
+			return -EOVERFLOW;
+	} else {
+		if (ia_valid & ATTR_UID &&
+		    !kfsuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
+			return -EOVERFLOW;
+		if (ia_valid & ATTR_GID &&
+		    !kfsgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
+			return -EOVERFLOW;
+	}
 
 	/* Don't allow modifications of files with invalid uids or
 	 * gids unless those uids & gids are being made valid.
-- 
2.25.0