From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935194AbeEWX1B (ORCPT ); Wed, 23 May 2018 19:27:01 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:48382 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935156AbeEWX0u (ORCPT ); Wed, 23 May 2018 19:26:50 -0400 From: "Eric W. Biederman" To: Linux Containers Cc: linux-fsdevel@vger.kernel.org, Seth Forshee , "Serge E. Hallyn" , Christian Brauner , linux-kernel@vger.kernel.org, "Eric W. Biederman" Date: Wed, 23 May 2018 18:25:37 -0500 Message-Id: <20180523232538.4880-5-ebiederm@xmission.com> X-Mailer: git-send-email 2.14.1 In-Reply-To: <87o9h6554f.fsf@xmission.com> References: <87o9h6554f.fsf@xmission.com> X-XM-SPF: eid=1fLd9c-0004ID-L7;;;mid=<20180523232538.4880-5-ebiederm@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=97.119.174.25;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18HpW5BPrTg4duoGHF2g1ZUqILm/2oIX6k= X-SA-Exim-Connect-IP: 97.119.174.25 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.7 XMSubLong Long Subject * 1.5 TR_Symld_Words too many words that have symbols inside * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5001] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_02 5+ unique symbols in subject * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ***;Linux Containers X-Spam-Relay-Country: X-Spam-Timing: total 600 ms - load_scoreonly_sql: 0.05 (0.0%), signal_user_changed: 3.0 (0.5%), b_tie_ro: 2.0 (0.3%), parse: 1.25 (0.2%), extract_message_metadata: 31 (5.1%), get_uri_detail_list: 3.3 (0.6%), tests_pri_-1000: 14 (2.3%), tests_pri_-950: 2.1 (0.4%), tests_pri_-900: 1.64 (0.3%), tests_pri_-400: 33 (5.6%), check_bayes: 32 (5.3%), b_tokenize: 13 (2.2%), b_tok_get_all: 8 (1.3%), b_comp_prob: 4.6 (0.8%), b_tok_touch_all: 2.9 (0.5%), b_finish: 0.81 (0.1%), tests_pri_0: 501 (83.6%), check_dkim_signature: 0.87 (0.1%), check_dkim_adsp: 5 (0.9%), tests_pri_500: 7 (1.2%), rewrite_mail: 0.00 (0.0%) Subject: [REVIEW][PATCH 5/6] capabilities: Allow privileged user in s_user_ns to set security.* xattrs X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A privileged user in s_user_ns will generally have the ability to manipulate the backing store and insert security.* xattrs into the filesystem directly. Therefore the kernel must be prepared to handle these xattrs from unprivileged mounts, and it makes little sense for commoncap to prevent writing these xattrs to the filesystem. The capability and LSM code have already been updated to appropriately handle xattrs from unprivileged mounts, so it is safe to loosen this restriction on setting xattrs. The exception to this logic is that writing xattrs to a mounted filesystem may also cause the LSM inode_post_setxattr or inode_setsecurity callbacks to be invoked. SELinux will deny the xattr update by virtue of applying mountpoint labeling to unprivileged userns mounts, and Smack will deny the writes for any user without global CAP_MAC_ADMIN, so loosening the capability check in commoncap is safe in this respect as well. Signed-off-by: Seth Forshee Acked-by: Serge Hallyn Signed-off-by: Eric W. Biederman --- security/commoncap.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/security/commoncap.c b/security/commoncap.c index 1ce701fcb3f3..f4c33abd9959 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -919,6 +919,8 @@ int cap_bprm_set_creds(struct linux_binprm *bprm) int cap_inode_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags) { + struct user_namespace *user_ns = dentry->d_sb->s_user_ns; + /* Ignore non-security xattrs */ if (strncmp(name, XATTR_SECURITY_PREFIX, sizeof(XATTR_SECURITY_PREFIX) - 1) != 0) @@ -931,7 +933,7 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name, if (strcmp(name, XATTR_NAME_CAPS) == 0) return 0; - if (!capable(CAP_SYS_ADMIN)) + if (!ns_capable(user_ns, CAP_SYS_ADMIN)) return -EPERM; return 0; } @@ -949,6 +951,8 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name, */ int cap_inode_removexattr(struct dentry *dentry, const char *name) { + struct user_namespace *user_ns = dentry->d_sb->s_user_ns; + /* Ignore non-security xattrs */ if (strncmp(name, XATTR_SECURITY_PREFIX, sizeof(XATTR_SECURITY_PREFIX) - 1) != 0) @@ -964,7 +968,7 @@ int cap_inode_removexattr(struct dentry *dentry, const char *name) return 0; } - if (!capable(CAP_SYS_ADMIN)) + if (!ns_capable(user_ns, CAP_SYS_ADMIN)) return -EPERM; return 0; } -- 2.14.1