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

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 [off-list ref] wrote:

On Sun, 18 Jul 2021 10:15:19 -0700
syzbot [off-list ref] wrote:

quoted

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 [off-list ref]
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