Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752935AbdHRNWA (ORCPT ); Fri, 18 Aug 2017 09:22:00 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:55702 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752921AbdHRNPy (ORCPT ); Fri, 18 Aug 2017 09:15:54 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, "Al Viro" , "Thomas Gleixner" , "syzkaller" , "Dmitry Vyukov" , "linux-fsdevel@vger.kernel.org"@decadent.org.uk Date: Fri, 18 Aug 2017 14:13:20 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 130/134] timerfd: Protect the might cancel mechanism proper In-Reply-To: X-SA-Exim-Connect-IP: 82.70.136.246 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2930 Lines: 94 3.16.47-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner commit 1e38da300e1e395a15048b0af1e5305bd91402f6 upstream. The handling of the might_cancel queueing is not properly protected, so parallel operations on the file descriptor can race with each other and lead to list corruptions or use after free. Protect the context for these operations with a seperate lock. The wait queue lock cannot be reused for this because that would create a lock inversion scenario vs. the cancel lock. Replacing might_cancel with an atomic (atomic_t or atomic bit) does not help either because it still can race vs. the actual list operation. Reported-by: Dmitry Vyukov Signed-off-by: Thomas Gleixner Cc: "linux-fsdevel@vger.kernel.org" Cc: syzkaller Cc: Al Viro Cc: linux-fsdevel@vger.kernel.org Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1701311521430.3457@nanos Signed-off-by: Thomas Gleixner Signed-off-by: Ben Hutchings --- fs/timerfd.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) --- a/fs/timerfd.c +++ b/fs/timerfd.c @@ -39,6 +39,7 @@ struct timerfd_ctx { int clockid; struct rcu_head rcu; struct list_head clist; + spinlock_t cancel_lock; bool might_cancel; }; @@ -111,7 +112,7 @@ void timerfd_clock_was_set(void) rcu_read_unlock(); } -static void timerfd_remove_cancel(struct timerfd_ctx *ctx) +static void __timerfd_remove_cancel(struct timerfd_ctx *ctx) { if (ctx->might_cancel) { ctx->might_cancel = false; @@ -121,6 +122,13 @@ static void timerfd_remove_cancel(struct } } +static void timerfd_remove_cancel(struct timerfd_ctx *ctx) +{ + spin_lock(&ctx->cancel_lock); + __timerfd_remove_cancel(ctx); + spin_unlock(&ctx->cancel_lock); +} + static bool timerfd_canceled(struct timerfd_ctx *ctx) { if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX) @@ -131,6 +139,7 @@ static bool timerfd_canceled(struct time static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags) { + spin_lock(&ctx->cancel_lock); if ((ctx->clockid == CLOCK_REALTIME || ctx->clockid == CLOCK_REALTIME_ALARM) && (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) { @@ -140,9 +149,10 @@ static void timerfd_setup_cancel(struct list_add_rcu(&ctx->clist, &cancel_list); spin_unlock(&cancel_lock); } - } else if (ctx->might_cancel) { - timerfd_remove_cancel(ctx); + } else { + __timerfd_remove_cancel(ctx); } + spin_unlock(&ctx->cancel_lock); } static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) @@ -326,6 +336,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clo return -ENOMEM; init_waitqueue_head(&ctx->wqh); + spin_lock_init(&ctx->cancel_lock); ctx->clockid = clockid; if (isalarm(ctx))