[PATCH v3 14/25] open: handle fsid mappings

From: Christian Brauner <christian.brauner@ubuntu.com>
To: "Stéphane Graber" <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 v3 14/25] open: handle fsid mappings
Date: Tue, 18 Feb 2020 15:34:00 +0100	[thread overview]
Message-ID: <20200218143411.2389182-15-christian.brauner@ubuntu.com> (raw)
In-Reply-To: <20200218143411.2389182-1-christian.brauner@ubuntu.com>

Let chown_common() 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.
do_faccessat() just needs to translate from real ids into fsids.

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

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
- Christian Brauner <christian.brauner@ubuntu.com>:
  - handle faccessat() too

/* v3 */
unchanged
---
 fs/open.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 0788b3715731..4e092845728f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -32,6 +32,7 @@
 #include <linux/ima.h>
 #include <linux/dnotify.h>
 #include <linux/compat.h>
+#include <linux/fsuidgid.h>
 
 #include "internal.h"
 
@@ -361,8 +362,10 @@ long do_faccessat(int dfd, const char __user *filename, int mode)
 	if (!override_cred)
 		return -ENOMEM;
 
-	override_cred->fsuid = override_cred->uid;
-	override_cred->fsgid = override_cred->gid;
+	override_cred->kfsuid = override_cred->uid;
+	override_cred->kfsgid = override_cred->gid;
+	override_cred->fsuid = kuid_to_kfsuid(override_cred->user_ns, override_cred->uid);
+	override_cred->fsgid = kgid_to_kfsgid(override_cred->user_ns, override_cred->gid);
 
 	if (!issecure(SECURE_NO_SETUID_FIXUP)) {
 		/* Clear the capabilities if we switch to a non-root user */
@@ -626,8 +629,13 @@ static int chown_common(const struct path *path, uid_t user, gid_t group)
 	kuid_t uid;
 	kgid_t gid;
 
-	uid = make_kuid(current_user_ns(), user);
-	gid = make_kgid(current_user_ns(), group);
+	if (is_userns_visible(inode->i_sb->s_iflags)) {
+		uid = make_kuid(current_user_ns(), user);
+		gid = make_kgid(current_user_ns(), group);
+	} else {
+		uid = make_kfsuid(current_user_ns(), user);
+		gid = make_kfsgid(current_user_ns(), group);
+	}
 
 retry_deleg:
 	newattrs.ia_valid =  ATTR_CTIME;
-- 
2.25.0

