linux-kernel - [PATCH 13/24] attr: notify_change(): handle fsid mappings

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Date:   Tue, 11 Feb 2020 17:57:42 +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 13/24] attr: notify_change(): handle fsid mappings

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@...ntu.com>
---
 fs/attr.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index df28035aa23e..3aa65165fb06 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)
 {
@@ -311,12 +313,21 @@ 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