From owner-svn-src-head@freebsd.org Sun Feb 16 03:14:56 2020 Return-Path: Delivered-To: svn-src-head@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 772AF2528AE; Sun, 16 Feb 2020 03:14:56 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 48Ksg36H9jz3MCm; Sun, 16 Feb 2020 03:14:55 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id D2CF61F49F; Sun, 16 Feb 2020 03:14:55 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 01G3EtsD074778; Sun, 16 Feb 2020 03:14:55 GMT (envelope-from mjg@FreeBSD.org) Received: (from mjg@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 01G3Ete9074777; Sun, 16 Feb 2020 03:14:55 GMT (envelope-from mjg@FreeBSD.org) Message-Id: <202002160314.01G3Ete9074777@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: mjg set sender to mjg@FreeBSD.org using -f From: Mateusz Guzik Date: Sun, 16 Feb 2020 03:14:55 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r357989 - head/sys/sys X-SVN-Group: head X-SVN-Commit-Author: mjg X-SVN-Commit-Paths: head/sys/sys X-SVN-Commit-Revision: 357989 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 16 Feb 2020 03:14:56 -0000 Author: mjg Date: Sun Feb 16 03:14:55 2020 New Revision: 357989 URL: https://svnweb.freebsd.org/changeset/base/357989 Log: refcount: add missing release fence to refcount_release_if_gt The CPU succeeding in releasing the not last reference can still have pending stores to the object protected by the affected counter. This opens a time window where another CPU can release the last reference and free the object, resulting in use-after-free. On top of that this prevents the compiler from generating more accesses to the object regardless of how atomic_fcmpset_rel_int is implemented (of course as long as it provides the release semantic). Reviewed by: markj Modified: head/sys/sys/refcount.h Modified: head/sys/sys/refcount.h ============================================================================== --- head/sys/sys/refcount.h Sun Feb 16 01:07:19 2020 (r357988) +++ head/sys/sys/refcount.h Sun Feb 16 03:14:55 2020 (r357989) @@ -198,7 +198,7 @@ refcount_release_if_gt(volatile u_int *count, u_int n) return (false); if (__predict_false(REFCOUNT_SATURATED(old))) return (true); - if (atomic_fcmpset_int(count, &old, old - 1)) + if (atomic_fcmpset_rel_int(count, &old, old - 1)) return (true); } }