Dimitri,

I am so pleased to get some support for fixing this bug that I will let
you manage things as you like.
Please perform necessary actions for proper achievement of our concern.
You have my approbation for any change you think is needed.

Regards,

Bernard


Le 20/01/2019 à 11:32, Dmitry Vyukov a écrit :

On Sun, Jan 20, 2019 at 10:58 AM f6bvp [off-list ref] wrote:

quoted

Hi,

Dmitry wrote:

quoted

Please also add:
Reported-by: syzbot+1a2c456a1ea08fa5b5f7@syzkaller.appspotmail.com

I did mention syzbot report but without the exact reference, thanks.

quoted

It's this report we are fixing, right?
https://syzkaller.appspot.com/bug?id=fd0b0b00fc26abb4b35663a0e2f1c91d8e6e5725

Yes exactly !
This is a long date well know bug I reported two years ago.

Then, well, I don't know, we either can leave syzbot as reporter if
you don't mind. Or don't include it as supports other means to
associate reports with fixes (#syz fix tag in email). The goal of
associating fixes with reports is to "close" bugs and get them off the
dashboard:
https://syzkaller.appspot.com/#upstream-open
Otherwise it turns into unuseful pile of bugs.

quoted

Bernard


On Sat, Jan 19, 2019 at 11:58 AM f6bvp [off-list ref] wrote:

quoted

[PATCH] [ROSE] NULL ax25_cb kernel panic

When an internally generated frame is handled by rose_xmit(),
rose_route_frame() is called:

        if (!rose_route_frame(skb, NULL)) {
                dev_kfree_skb(skb);
                stats->tx_errors++;
                return NETDEV_TX_OK;
        }

We have the same code sequence in Net/Rom where an internally generated
frame is handled by nr_xmit() calling nr_route_frame(skb, NULL).
However, in this function NULL argument is tested while it is not in
rose_route_frame().
Then kernel panic occurs later on when calling ax25cmp() with a NULL
ax25_cb argument as reported many times and recently with syzbot.

We need to test if ax25 is NULL before using it.

Here is the patch:

diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
index 77e9f85a2c92..7f075255a372 100644
--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c

@@ -850,6 +850,7 @@ void rose_link_device_down(struct net_device *dev)

 /*
  *     Route a frame to an appropriate AX.25 connection.
+ *     a NULL ax25_cb indicates an internally generated frame.
  */
 int rose_route_frame(struct sk_buff *skb, ax25_cb *ax25)
 {

@@ -867,6 +868,10 @@ int rose_route_frame(struct sk_buff *skb, ax25_cb

*ax25)

        if (skb->len < ROSE_MIN_LEN)
                return res;
+
+       if (!ax25)
+               return rose_loopback_queue(skb, NULL);
+
        frametype = skb->data[2];
        lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) &

0x0FF);

quoted

        if (frametype == ROSE_CALL_REQUEST &&

Signed-off-by: Bernard Pidoux, f6bvp <redacted>

Please also add:

Reported-by: syzbot+1a2c456a1ea08fa5b5f7@syzkaller.appspotmail.com

It's this report we are fixing, right?
https://syzkaller.appspot.com/bug?id=fd0b0b00fc26abb4b35663a0e2f1c91d8e6e5725