2019-01-25 10:48:22

by Dmitry Vyukov

Subject: [PATCH] net/rose: fix NULL ax25_cb kernel panic

From: Bernard Pidoux <[email protected]>

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.

Testing:
Built kernel with CONFIG_ROSE=y.

Signed-off-by: Bernard Pidoux <[email protected]>
Acked-by: Dmitry Vyukov <[email protected]>
Reported-by: [email protected]
Cc: "David S. Miller" <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Bernard Pidoux <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
net/rose/rose_route.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
index 77e9f85a2c92..f2ff21d7df08 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);
if (frametype == ROSE_CALL_REQUEST &&
--
2.20.1.495.gaa96b0ce6b-goog

2019-01-27 18:42:22

by David Miller

Subject: Re: [PATCH] net/rose: fix NULL ax25_cb kernel panic

From: Dmitry Vyukov <[email protected]>
Date: Fri, 25 Jan 2019 11:46:40 +0100

> From: Bernard Pidoux <[email protected]>
>
> 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.
>
> Testing:
> Built kernel with CONFIG_ROSE=y.
>
> Signed-off-by: Bernard Pidoux <[email protected]>
> Acked-by: Dmitry Vyukov <[email protected]>
> Reported-by: [email protected]

Applied and queued up for -stable, thanks.