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![Ondrej Mosnacek](/assets/img/avatar_default.png)
This is motivated by a perfomance regression of selinux_xfrm_enabled() that happened on a RHEL kernel due to false sharing between selinux_xfrm_refcount and (the late) selinux_ss.policy_rwlock (i.e. the .bss section memory layout changed such that they happened to share the same cacheline). Since the policy rwlock's memory region was modified upon each read-side critical section, the readers of selinux_xfrm_refcount had frequent cache misses, eventually leading to a significant performance degradation under a TCP SYN flood on a system with many cores (32 in this case, but it's detectable on less cores as well). While upstream has since switched to RCU locking, so the same can no longer happen here, selinux_xfrm_refcount could still share a cacheline with another frequently written region, thus marking it __read_mostly still makes sense. __read_mostly helps, because it will put the symbol in a separate section along with other read-mostly variables, so there should never be a clash with frequently written data. Since selinux_xfrm_refcount is modified only in case of an explicit action, it should be safe to do this (i.e. it shouldn't disrupt other read-mostly variables too much). Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com> Signed-off-by: Paul Moore <paul@paul-moore.com>
473 lines
11 KiB
C
473 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* NSA Security-Enhanced Linux (SELinux) security module
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*
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* This file contains the SELinux XFRM hook function implementations.
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*
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* Authors: Serge Hallyn <sergeh@us.ibm.com>
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* Trent Jaeger <jaegert@us.ibm.com>
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*
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* Updated: Venkat Yekkirala <vyekkirala@TrustedCS.com>
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*
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* Granular IPSec Associations for use in MLS environments.
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*
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* Copyright (C) 2005 International Business Machines Corporation
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* Copyright (C) 2006 Trusted Computer Solutions, Inc.
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*/
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/*
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* USAGE:
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* NOTES:
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* 1. Make sure to enable the following options in your kernel config:
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* CONFIG_SECURITY=y
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* CONFIG_SECURITY_NETWORK=y
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* CONFIG_SECURITY_NETWORK_XFRM=y
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* CONFIG_SECURITY_SELINUX=m/y
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* ISSUES:
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* 1. Caching packets, so they are not dropped during negotiation
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* 2. Emulating a reasonable SO_PEERSEC across machines
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* 3. Testing addition of sk_policy's with security context via setsockopt
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*/
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/security.h>
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#include <linux/types.h>
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#include <linux/slab.h>
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#include <linux/ip.h>
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#include <linux/tcp.h>
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#include <linux/skbuff.h>
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#include <linux/xfrm.h>
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#include <net/xfrm.h>
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#include <net/checksum.h>
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#include <net/udp.h>
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#include <linux/atomic.h>
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#include "avc.h"
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#include "objsec.h"
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#include "xfrm.h"
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/* Labeled XFRM instance counter */
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atomic_t selinux_xfrm_refcount __read_mostly = ATOMIC_INIT(0);
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/*
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* Returns true if the context is an LSM/SELinux context.
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*/
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static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
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{
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return (ctx &&
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(ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
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(ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
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}
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/*
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* Returns true if the xfrm contains a security blob for SELinux.
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*/
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static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
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{
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return selinux_authorizable_ctx(x->security);
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}
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/*
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* Allocates a xfrm_sec_state and populates it using the supplied security
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* xfrm_user_sec_ctx context.
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*/
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static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
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struct xfrm_user_sec_ctx *uctx,
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gfp_t gfp)
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{
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int rc;
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const struct task_security_struct *tsec = selinux_cred(current_cred());
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struct xfrm_sec_ctx *ctx = NULL;
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u32 str_len;
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if (ctxp == NULL || uctx == NULL ||
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uctx->ctx_doi != XFRM_SC_DOI_LSM ||
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uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
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return -EINVAL;
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str_len = uctx->ctx_len;
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if (str_len >= PAGE_SIZE)
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return -ENOMEM;
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ctx = kmalloc(sizeof(*ctx) + str_len + 1, gfp);
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if (!ctx)
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return -ENOMEM;
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ctx->ctx_doi = XFRM_SC_DOI_LSM;
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ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
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ctx->ctx_len = str_len;
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memcpy(ctx->ctx_str, &uctx[1], str_len);
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ctx->ctx_str[str_len] = '\0';
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rc = security_context_to_sid(&selinux_state, ctx->ctx_str, str_len,
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&ctx->ctx_sid, gfp);
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if (rc)
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goto err;
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rc = avc_has_perm(&selinux_state,
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tsec->sid, ctx->ctx_sid,
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SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
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if (rc)
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goto err;
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*ctxp = ctx;
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atomic_inc(&selinux_xfrm_refcount);
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return 0;
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err:
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kfree(ctx);
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return rc;
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}
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/*
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* Free the xfrm_sec_ctx structure.
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*/
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static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
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{
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if (!ctx)
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return;
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atomic_dec(&selinux_xfrm_refcount);
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kfree(ctx);
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}
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/*
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* Authorize the deletion of a labeled SA or policy rule.
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*/
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static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
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{
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const struct task_security_struct *tsec = selinux_cred(current_cred());
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if (!ctx)
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return 0;
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return avc_has_perm(&selinux_state,
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tsec->sid, ctx->ctx_sid,
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SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
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NULL);
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}
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/*
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* LSM hook implementation that authorizes that a flow can use a xfrm policy
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* rule.
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*/
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int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
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{
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int rc;
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/* All flows should be treated as polmatch'ing an otherwise applicable
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* "non-labeled" policy. This would prevent inadvertent "leaks". */
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if (!ctx)
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return 0;
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/* Context sid is either set to label or ANY_ASSOC */
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if (!selinux_authorizable_ctx(ctx))
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return -EINVAL;
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rc = avc_has_perm(&selinux_state,
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fl_secid, ctx->ctx_sid,
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SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
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return (rc == -EACCES ? -ESRCH : rc);
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}
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/*
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* LSM hook implementation that authorizes that a state matches
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* the given policy, flow combo.
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*/
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int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
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struct xfrm_policy *xp,
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const struct flowi_common *flic)
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{
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u32 state_sid;
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u32 flic_sid;
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if (!xp->security)
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if (x->security)
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/* unlabeled policy and labeled SA can't match */
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return 0;
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else
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/* unlabeled policy and unlabeled SA match all flows */
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return 1;
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else
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if (!x->security)
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/* unlabeled SA and labeled policy can't match */
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return 0;
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else
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if (!selinux_authorizable_xfrm(x))
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/* Not a SELinux-labeled SA */
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return 0;
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state_sid = x->security->ctx_sid;
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flic_sid = flic->flowic_secid;
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if (flic_sid != state_sid)
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return 0;
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/* We don't need a separate SA Vs. policy polmatch check since the SA
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* is now of the same label as the flow and a flow Vs. policy polmatch
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* check had already happened in selinux_xfrm_policy_lookup() above. */
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return (avc_has_perm(&selinux_state, flic_sid, state_sid,
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SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
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NULL) ? 0 : 1);
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}
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static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
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{
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struct dst_entry *dst = skb_dst(skb);
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struct xfrm_state *x;
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if (dst == NULL)
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return SECSID_NULL;
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x = dst->xfrm;
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if (x == NULL || !selinux_authorizable_xfrm(x))
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return SECSID_NULL;
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return x->security->ctx_sid;
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}
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static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
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u32 *sid, int ckall)
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{
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u32 sid_session = SECSID_NULL;
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struct sec_path *sp = skb_sec_path(skb);
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if (sp) {
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int i;
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for (i = sp->len - 1; i >= 0; i--) {
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struct xfrm_state *x = sp->xvec[i];
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if (selinux_authorizable_xfrm(x)) {
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struct xfrm_sec_ctx *ctx = x->security;
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if (sid_session == SECSID_NULL) {
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sid_session = ctx->ctx_sid;
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if (!ckall)
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goto out;
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} else if (sid_session != ctx->ctx_sid) {
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*sid = SECSID_NULL;
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return -EINVAL;
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}
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}
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}
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}
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out:
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*sid = sid_session;
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return 0;
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}
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/*
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* LSM hook implementation that checks and/or returns the xfrm sid for the
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* incoming packet.
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*/
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int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
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{
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if (skb == NULL) {
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*sid = SECSID_NULL;
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return 0;
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}
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return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
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}
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int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
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{
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int rc;
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rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
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if (rc == 0 && *sid == SECSID_NULL)
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*sid = selinux_xfrm_skb_sid_egress(skb);
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return rc;
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}
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/*
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* LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
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*/
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int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
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struct xfrm_user_sec_ctx *uctx,
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gfp_t gfp)
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{
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return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
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}
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/*
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* LSM hook implementation that copies security data structure from old to new
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* for policy cloning.
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*/
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int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
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struct xfrm_sec_ctx **new_ctxp)
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{
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struct xfrm_sec_ctx *new_ctx;
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if (!old_ctx)
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return 0;
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new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
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GFP_ATOMIC);
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if (!new_ctx)
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return -ENOMEM;
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atomic_inc(&selinux_xfrm_refcount);
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*new_ctxp = new_ctx;
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return 0;
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}
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/*
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* LSM hook implementation that frees xfrm_sec_ctx security information.
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*/
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void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
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{
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selinux_xfrm_free(ctx);
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}
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/*
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* LSM hook implementation that authorizes deletion of labeled policies.
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*/
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int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
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{
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return selinux_xfrm_delete(ctx);
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}
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/*
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* LSM hook implementation that allocates a xfrm_sec_state, populates it using
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* the supplied security context, and assigns it to the xfrm_state.
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*/
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int selinux_xfrm_state_alloc(struct xfrm_state *x,
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struct xfrm_user_sec_ctx *uctx)
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{
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return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
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}
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/*
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* LSM hook implementation that allocates a xfrm_sec_state and populates based
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* on a secid.
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*/
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int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
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struct xfrm_sec_ctx *polsec, u32 secid)
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{
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int rc;
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struct xfrm_sec_ctx *ctx;
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char *ctx_str = NULL;
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int str_len;
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if (!polsec)
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return 0;
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if (secid == 0)
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return -EINVAL;
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rc = security_sid_to_context(&selinux_state, secid, &ctx_str,
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&str_len);
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if (rc)
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return rc;
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ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
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if (!ctx) {
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rc = -ENOMEM;
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goto out;
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}
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ctx->ctx_doi = XFRM_SC_DOI_LSM;
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ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
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ctx->ctx_sid = secid;
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ctx->ctx_len = str_len;
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memcpy(ctx->ctx_str, ctx_str, str_len);
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x->security = ctx;
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atomic_inc(&selinux_xfrm_refcount);
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out:
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kfree(ctx_str);
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return rc;
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}
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/*
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* LSM hook implementation that frees xfrm_state security information.
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*/
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void selinux_xfrm_state_free(struct xfrm_state *x)
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{
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selinux_xfrm_free(x->security);
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}
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/*
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* LSM hook implementation that authorizes deletion of labeled SAs.
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*/
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int selinux_xfrm_state_delete(struct xfrm_state *x)
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{
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return selinux_xfrm_delete(x->security);
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}
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/*
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* LSM hook that controls access to unlabelled packets. If
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* a xfrm_state is authorizable (defined by macro) then it was
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* already authorized by the IPSec process. If not, then
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* we need to check for unlabelled access since this may not have
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* gone thru the IPSec process.
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*/
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int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
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struct common_audit_data *ad)
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{
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int i;
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struct sec_path *sp = skb_sec_path(skb);
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u32 peer_sid = SECINITSID_UNLABELED;
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if (sp) {
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for (i = 0; i < sp->len; i++) {
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struct xfrm_state *x = sp->xvec[i];
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if (x && selinux_authorizable_xfrm(x)) {
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struct xfrm_sec_ctx *ctx = x->security;
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peer_sid = ctx->ctx_sid;
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break;
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}
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}
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}
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/* This check even when there's no association involved is intended,
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* according to Trent Jaeger, to make sure a process can't engage in
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* non-IPsec communication unless explicitly allowed by policy. */
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return avc_has_perm(&selinux_state,
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sk_sid, peer_sid,
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SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
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}
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/*
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* POSTROUTE_LAST hook's XFRM processing:
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* If we have no security association, then we need to determine
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* whether the socket is allowed to send to an unlabelled destination.
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* If we do have a authorizable security association, then it has already been
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* checked in the selinux_xfrm_state_pol_flow_match hook above.
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*/
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int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
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struct common_audit_data *ad, u8 proto)
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{
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struct dst_entry *dst;
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switch (proto) {
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case IPPROTO_AH:
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case IPPROTO_ESP:
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case IPPROTO_COMP:
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/* We should have already seen this packet once before it
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* underwent xfrm(s). No need to subject it to the unlabeled
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* check. */
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return 0;
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default:
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break;
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}
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dst = skb_dst(skb);
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if (dst) {
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struct dst_entry *iter;
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for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
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struct xfrm_state *x = iter->xfrm;
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if (x && selinux_authorizable_xfrm(x))
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return 0;
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}
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}
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/* This check even when there's no association involved is intended,
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* according to Trent Jaeger, to make sure a process can't engage in
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* non-IPsec communication unless explicitly allowed by policy. */
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return avc_has_perm(&selinux_state, sk_sid, SECINITSID_UNLABELED,
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SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
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}
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