linux-kernel - [PATCH 3.12 60/78] userns: Don't allow unprivileged creation of gid mappings

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Date:	Fri,  9 Jan 2015 11:32:09 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 60/78] userns: Don't allow unprivileged creation of gid mappings

From: "Eric W. Biederman" <ebiederm@...ssion.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit be7c6dba2332cef0677fbabb606e279ae76652c3 upstream.

As any gid mapping will allow and must allow for backwards
compatibility dropping groups don't allow any gid mappings to be
established without CAP_SETGID in the parent user namespace.

For a small class of applications this change breaks userspace
and removes useful functionality.  This small class of applications
includes tools/testing/selftests/mount/unprivilged-remount-test.c

Most of the removed functionality will be added back with the addition
of a one way knob to disable setgroups.  Once setgroups is disabled
setting the gid_map becomes as safe as setting the uid_map.

For more common applications that set the uid_map and the gid_map
with privilege this change will have no affect.

This is part of a fix for CVE-2014-8989.

Reviewed-by: Andy Lutomirski <luto@...capital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/user_namespace.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 048bb7b641a9..a5809c42a1b3 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -808,11 +808,6 @@ static bool new_idmap_permitted(const struct file *file,
 			if (uid_eq(uid, file->f_cred->fsuid))
 				return true;
 		}
-		else if (cap_setid == CAP_SETGID) {
-			kgid_t gid = make_kgid(ns->parent, id);
-			if (gid_eq(gid, file->f_cred->fsgid))
-				return true;
-		}
 	}

 	/* Allow anyone to set a mapping that doesn't require privilege */
-- 
2.2.1

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