Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932649AbcDBBKm (ORCPT ); Fri, 1 Apr 2016 21:10:42 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:54514 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755812AbcDBA5A (ORCPT ); Fri, 1 Apr 2016 20:57:00 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Alexander Potapenko , Eric Dumazet , Kostya Serebryany , Sasha Levin , Arnaldo Carvalho de Melo , "David S . Miller" , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 128/170] net: Fix use after free in the recvmmsg exit path Date: Fri, 1 Apr 2016 17:53:34 -0700 Message-Id: <1459558456-24452-129-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1459558456-24452-1-git-send-email-kamal@canonical.com> References: <1459558456-24452-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2977 Lines: 94 3.19.8-ckt18 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Arnaldo Carvalho de Melo commit 34b88a68f26a75e4fded796f1a49c40f82234b7d upstream. The syzkaller fuzzer hit the following use-after-free: Call Trace: [] __asan_report_load8_noabort+0x3e/0x40 mm/kasan/report.c:295 [] __sys_recvmmsg+0x6fa/0x7f0 net/socket.c:2261 [< inline >] SYSC_recvmmsg net/socket.c:2281 [] SyS_recvmmsg+0x16f/0x180 net/socket.c:2270 [] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185 And, as Dmitry rightly assessed, that is because we can drop the reference and then touch it when the underlying recvmsg calls return some packets and then hit an error, which will make recvmmsg to set sock->sk->sk_err, oops, fix it. Reported-and-Tested-by: Dmitry Vyukov Cc: Alexander Potapenko Cc: Eric Dumazet Cc: Kostya Serebryany Cc: Sasha Levin Fixes: a2e2725541fa ("net: Introduce recvmmsg socket syscall") http://lkml.kernel.org/r/20160122211644.GC2470@redhat.com Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: David S. Miller Signed-off-by: Kamal Mostafa --- net/socket.c | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/net/socket.c b/net/socket.c index d50e7ca..c09c417 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2387,31 +2387,31 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen, break; } -out_put: - fput_light(sock->file, fput_needed); - if (err == 0) - return datagrams; + goto out_put; - if (datagrams != 0) { + if (datagrams == 0) { + datagrams = err; + goto out_put; + } + + /* + * We may return less entries than requested (vlen) if the + * sock is non block and there aren't enough datagrams... + */ + if (err != -EAGAIN) { /* - * We may return less entries than requested (vlen) if the - * sock is non block and there aren't enough datagrams... + * ... or if recvmsg returns an error after we + * received some datagrams, where we record the + * error to return on the next call or if the + * app asks about it using getsockopt(SO_ERROR). */ - if (err != -EAGAIN) { - /* - * ... or if recvmsg returns an error after we - * received some datagrams, where we record the - * error to return on the next call or if the - * app asks about it using getsockopt(SO_ERROR). - */ - sock->sk->sk_err = -err; - } - - return datagrams; + sock->sk->sk_err = -err; } +out_put: + fput_light(sock->file, fput_needed); - return err; + return datagrams; } SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg, -- 2.7.4