From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933875Ab1DNSLN (ORCPT ); Thu, 14 Apr 2011 14:11:13 -0400 Received: from mail.windriver.com ([147.11.1.11]:42085 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933658Ab1DNR63 (ORCPT ); Thu, 14 Apr 2011 13:58:29 -0400 From: Paul Gortmaker To: stable@kernel.org, linux-kernel@vger.kernel.org Cc: stable-review@kernel.org, NeilBrown , "J. Bruce Fields" , Paul Gortmaker Subject: [34-longterm 165/209] sunrpc: prevent use-after-free on clearing XPT_BUSY Date: Thu, 14 Apr 2011 13:55:23 -0400 Message-Id: <1302803767-9715-52-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.4.4 In-Reply-To: <1302803767-9715-1-git-send-email-paul.gortmaker@windriver.com> References: <1302803039-9400-1-git-send-email-paul.gortmaker@windriver.com> <1302803767-9715-1-git-send-email-paul.gortmaker@windriver.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: NeilBrown ===================================================================== | This is a commit scheduled for the next v2.6.34 longterm release. | | If you see a problem with using this for longterm, please comment.| ===================================================================== commit ed2849d3ecfa339435818eeff28f6c3424300cec upstream. When an xprt is created, it has a refcount of 1, and XPT_BUSY is set. The refcount is *not* owned by the thread that created the xprt (as is clear from the fact that creators never put the reference). Rather, it is owned by the absence of XPT_DEAD. Once XPT_DEAD is set, (And XPT_BUSY is clear) that initial reference is dropped and the xprt can be freed. So when a creator clears XPT_BUSY it is dropping its only reference and so must not touch the xprt again. However svc_recv, after calling ->xpo_accept (and so getting an XPT_BUSY reference on a new xprt), calls svc_xprt_recieved. This clears XPT_BUSY and then svc_xprt_enqueue - this last without owning a reference. This is dangerous and has been seen to leave svc_xprt_enqueue working with an xprt containing garbage. So we need to hold an extra counted reference over that call to svc_xprt_received. For safety, any time we clear XPT_BUSY and then use the xprt again, we first get a reference, and the put it again afterwards. Note that svc_close_all does not need this extra protection as there are no threads running, and the final free can only be called asynchronously from such a thread. Signed-off-by: NeilBrown Signed-off-by: J. Bruce Fields Signed-off-by: Paul Gortmaker --- net/sunrpc/svc_xprt.c | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-) diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index 061b2e0..aa1d2c6 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -212,6 +212,7 @@ int svc_create_xprt(struct svc_serv *serv, const char *xprt_name, spin_lock(&svc_xprt_class_lock); list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) { struct svc_xprt *newxprt; + unsigned short newport; if (strcmp(xprt_name, xcl->xcl_name)) continue; @@ -230,8 +231,9 @@ int svc_create_xprt(struct svc_serv *serv, const char *xprt_name, spin_lock_bh(&serv->sv_lock); list_add(&newxprt->xpt_list, &serv->sv_permsocks); spin_unlock_bh(&serv->sv_lock); + newport = svc_xprt_local_port(newxprt); clear_bit(XPT_BUSY, &newxprt->xpt_flags); - return svc_xprt_local_port(newxprt); + return newport; } err: spin_unlock(&svc_xprt_class_lock); @@ -431,8 +433,13 @@ void svc_xprt_received(struct svc_xprt *xprt) { BUG_ON(!test_bit(XPT_BUSY, &xprt->xpt_flags)); xprt->xpt_pool = NULL; + /* As soon as we clear busy, the xprt could be closed and + * 'put', so we need a reference to call svc_xprt_enqueue with: + */ + svc_xprt_get(xprt); clear_bit(XPT_BUSY, &xprt->xpt_flags); svc_xprt_enqueue(xprt); + svc_xprt_put(xprt); } EXPORT_SYMBOL_GPL(svc_xprt_received); -- 1.7.4.4