Re: [syzbot] KASAN: use-after-free Read in tipc_recvmsg

From: Xin Long <lucien.xin@gmail.com>
To: Pavel Skripkin <paskripkin@gmail.com>
Cc: syzbot <syzbot+e6741b97d5552f97c24d@syzkaller.appspotmail.com>,
	davem <davem@davemloft.net>,
	devicetree@vger.kernel.org, frowand.list@gmail.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jon Maloy <jmaloy@redhat.com>, Jakub Kicinski <kuba@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	network dev <netdev@vger.kernel.org>,
	rafael@kernel.org, robh+dt@kernel.org, robh@kernel.org,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	tipc-discussion@lists.sourceforge.net,
	Ying Xue <ying.xue@windriver.com>
Subject: Re: [syzbot] KASAN: use-after-free Read in tipc_recvmsg
Date: Fri, 23 Jul 2021 12:41:46 -0400	[thread overview]
Message-ID: <CADvbK_dkv-DDt_VSSn1NQnzrUuxPm0T2Mki46T0jdwfUxENW-Q@mail.gmail.com> (raw)
In-Reply-To: <20210723193611.746e7071@gmail.com>

a fix already posted in tipc-discussion:

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 9b0b311c7ec1..b0dd183a4dbc 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -1973,10 +1973,12 @@ static int tipc_recvmsg(struct socket *sock,
struct msghdr *m,
                tipc_node_distr_xmit(sock_net(sk), &xmitq);
        }

-       if (!skb_cb->bytes_read)
-               tsk_advance_rx_queue(sk);
+       if (skb_cb->bytes_read)
+               goto exit;
+
+       tsk_advance_rx_queue(sk);

-       if (likely(!connected) || skb_cb->bytes_read)
+       if (likely(!connected))
                goto exit;

On Fri, Jul 23, 2021 at 12:38 PM Pavel Skripkin <paskripkin@gmail.com> wrote:
>
> On Sun, 18 Jul 2021 10:15:19 -0700
> syzbot <syzbot+e6741b97d5552f97c24d@syzkaller.appspotmail.com> wrote:
>
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    ab0441b4a920 Merge branch 'vmxnet3-version-6'
> > git tree:       net-next
> > console output:
> > https://syzkaller.appspot.com/x/log.txt?x=1744ac6a300000 kernel
> > config:  https://syzkaller.appspot.com/x/.config?x=da140227e4f25b17
> > dashboard link:
> > https://syzkaller.appspot.com/bug?extid=e6741b97d5552f97c24d syz
> > repro:
> > https://syzkaller.appspot.com/x/repro.syz?x=13973a74300000 C
> > reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ffc902300000
> >
> > The issue was bisected to:
> >
> > commit 67a3156453859ceb40dc4448b7a6a99ea0ad27c7
> > Author: Rob Herring <robh@kernel.org>
> > Date:   Thu May 27 19:45:47 2021 +0000
> >
> >     of: Merge of_address_to_resource() and
> > of_pci_address_to_resource() implementations
> >
> > bisection log:
> > https://syzkaller.appspot.com/x/bisect.txt?x=129b0438300000 final
> > oops:     https://syzkaller.appspot.com/x/report.txt?x=119b0438300000
> > console output:
> > https://syzkaller.appspot.com/x/log.txt?x=169b0438300000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the
> > commit: Reported-by:
> > syzbot+e6741b97d5552f97c24d@syzkaller.appspotmail.com Fixes:
> > 67a315645385 ("of: Merge of_address_to_resource() and
> > of_pci_address_to_resource() implementations")
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in tipc_recvmsg+0xf77/0xf90
> > net/tipc/socket.c:1979 Read of size 4 at addr ffff8880328cf1c0 by
> > task kworker/u4:0/8
> >
>
> Since code accesing skb_cb after possible kfree_skb() call let's just
> store bytes_read to variable and use it instead of acessing
> skb_cb->bytes_read
>
> #syz test
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
>
>
> With regards,
> Pavel Skripkin
