Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753179AbcDVL3H (ORCPT ); Fri, 22 Apr 2016 07:29:07 -0400 Received: from mx2.suse.de ([195.135.220.15]:43942 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753243AbcDVLGP (ORCPT ); Fri, 22 Apr 2016 07:06:15 -0400 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo , Alexander Potapenko , Eric Dumazet , Kostya Serebryany , Sasha Levin , "David S . Miller" , Jiri Slaby Subject: [PATCH 3.12 26/78] net: Fix use after free in the recvmmsg exit path Date: Fri, 22 Apr 2016 13:05:09 +0200 Message-Id: <2c7a8d368b3bef1cf97ea000ba0c07b27562af15.1461323133.git.jslaby@suse.cz> X-Mailer: git-send-email 2.8.1 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2923 Lines: 94 From: Arnaldo Carvalho de Melo 3.12-stable review patch. If anyone has any objections, please let me know. =============== [ Upstream commit 34b88a68f26a75e4fded796f1a49c40f82234b7d ] 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: Jiri Slaby --- net/socket.c | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/net/socket.c b/net/socket.c index 00634623573f..64c47cd62e14 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2389,31 +2389,31 @@ 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, -- 2.8.1