rose_route_frame() NULL pointer dereference kernel panic

[Patch] Null pointer in rose_route_frame()

Bug appears when setting a second IP to ethernet device without adding a route and a gateway:

/sbin/ifconfig enp4s0:1 44.168.19.22 netmask 255.255.255.240

If a route and a gateway are not added for subnet, and if ax25ipd configuration includes a destination address in this subnet, then a comparison of destinations address performed by ax25cmp() called by rose_route_frame() is facing a null pointer and a kernel panic occurs.

Attached is the report of kernel panic followed by a report of successful patched function.

Bernard

==================================
6,756,516974441,-;NET: Registered protocol family 3 6,757,516978403,-;mkiss: AX.25 Multikiss, Hans Albas PE1AYX 6,758,516979388,-;mkiss: ax0: crc mode is auto.
6,759,516979945,-;IPv6: ADDRCONF(NETDEV_CHANGE): ax0: link becomes ready 6,760,519023446,-;NET: Registered protocol family 11 6,761,522043100,-;mkiss: ax0: Trying crc-smack
6,762,522044882,-;mkiss: ax0: Trying crc-flexnet
1,763,522044973,c;BUG: unable to handle kernel
4,764,522044974,+;NULL pointer dereference
4,765,522044975,+; at 0000000000000017
1,766,522044976,c;IP:
4,767,522044986,+; [<ffffffffc05ad0a9>] ax25cmp+0x19/0x60 [ax25] 4,768,522044987,c;PGD 3cd61067
4,769,522044987,+;PUD 35ac0067
4,770,522044988,+;PMD 0
4,771,522044989,+;
4,772,522044990,c;Oops: 0000 [#1]
4,773,522044991,+;SMP
4,774,522044991,+;
4,775,522044994,c;Modules linked in:
4,776,522044995,+; rose
4,777,522044996,+; mkiss
4,778,522044996,+; ax25
4,779,522044997,+; netconsole
4,846,522045047,+;
4,847,522045050,-;CPU: 1 PID: 11873 Comm: ax25ipd Not tainted 4.4.1 #2
4,848,522045051,-;Hardware name: /D975XBX2, BIOS BX97520J.86A.2797.2007.1008.1941 10/08/2007
4,849,522045053,-;task: ffff880037beb500 ti: ffff880034320000 task.ti: ffff880034320000 4,850,522045055,c;RIP: 0010:[<ffffffffc05ad0a9>]
4,851,522045058,+; [<ffffffffc05ad0a9>] ax25cmp+0x19/0x60 [ax25] 4,852,522045059,-;RSP: 0018:ffff880034323938 EFLAGS: 00010246 4,876,522045080,+;
4,877,522045081,-;Call Trace:
4,878,522045088,-; [<ffffffffc05cde6c>] rose_route_frame+0x9c/0x670 [rose] 4,879,522045094,-; [<ffffffff810aef90>] ? __init_waitqueue_head+0x10/0x20 4,971,522045204,+;
0,978,522045215,-;Kernel panic - not syncing: Fatal exception in interrupt 0,979,522045763,-;Kernel Offset: disabled
0,980,522045763,c;Rebooting in 30 seconds..

After patch is applied :
6,767,4251903518,-;NET: Registered protocol family 3 6,768,4251907330,-;mkiss: AX.25 Multikiss, Hans Albas PE1AYX 6,769,4251908399,-;mkiss: ax0: crc mode is auto. 6,770,4251909044,-;IPv6: ADDRCONF(NETDEV_CHANGE): ax0: link becomes ready 6,771,4253957114,-;NET: Registered protocol family 11 6,772,4256972259,-;mkiss: ax0: Trying crc-smack 6,773,4256974292,-;mkiss: ax0: Trying crc-flexnet 4,774,4256974372,-;Null ax25 destination ! 4,775,4256978218,-;Null ax25 destination ! 4,776,4266975133,-;Null ax25 destination ! 4,777,4267007092,-;Null ax25 destination ! 4,778,4287007148,-;Null ax25 destination !

index 0fc76d8..254e528 100644
@@ -863,6 +863,11 @@ int rose_route_frame(struct sk_buff *skb, ax25_cb *ax25)
        int res = 0;
        char buf[11];
 
+       if (ax25 == NULL) {
+               printk("Null ax25 destination !\n");
+               return res;
+       }
+
        if (skb->len < ROSE_MIN_LEN)
                return res;
        frametype = skb->data[2];

Hi All,

I further investigated the null pointer bug After David Miller on linux-netdev noticed rose_route_frame() being called by rose_xmit() with an explicit NULL argument.

Here is the explanation :

When rose_route_frame() is called by rose_xmit() with
NULL *ax25 argument the following comparison (rose_route.c , line 883)

if (ax25cmp(&ax25->dest_addr, &rose_neigh->callsign) == 0 &&

always has a pointer dereference leading to a kernel panic.

I noticed, using a few printk, that during rose normal operations rose_xmit() was never called when ax25ipd sends an UDP frame. Otherwise, this bug would have been found earlier.
It is only because FPAC application asked for a connection to an address without defined route and gateway that rose_xmit() was activated.

I am not sure I understood well the purpose of the NULL second argument. I only guess it was intended to have ax25->dest_addr empty in order to make the comparison with all possible rose_neigh->callsign always false.

I built the following patch in order to obtain the same result without NULL pointer.

@@ -101,13 +101,16 @@ static netdev_tx_t rose_xmit(struct sk_b
 {
        struct net_device_stats *stats = &dev->stats;
        unsigned int len = skb->len;
+       struct ax25_cb ax25;
 
+       memset(&ax25, 0, sizeof(struct ax25_cb));
+
        if (!netif_running(dev)) {
                printk(KERN_ERR "ROSE: rose_xmit - called when iface is 

down\n");
                return NETDEV_TX_BUSY;
        }

- if (!rose_route_frame(skb, NULL)) {

+       if (!rose_route_frame(skb, &ax25)) {
                dev_kfree_skb(skb);
                stats->tx_errors++;
                return NETDEV_TX_OK;

After this patch is applied, the following was captured

[ 1786.971744] NET: Registered protocol family 3
[ 1786.990288] mkiss: AX.25 Multikiss, Hans Albas PE1AYX
[ 1786.991179] mkiss: ax0: crc mode is auto.
[ 1786.991585] IPv6: ADDRCONF(NETDEV_CHANGE): ax0: link becomes ready
[ 1789.270858] NET: Registered protocol family 11
[ 1792.286229] mkiss: ax0: Trying crc-smack
[ 1792.287588] mkiss: ax0: Trying crc-flexnet
[ 1792.287650] rose_route : unknown neighbour or device *
[ 1792.290174] rose_route : unknown neighbour or device *
[ 1802.304145] rose_route : unknown neighbour or device *
[ 1802.305516] rose_route : unknown neighbour or device *
[ 1818.496876] IPv4: martian source 255.255.255.255 from 44.168.19.17, on dev enp4s0
[ 1818.498115] ll header: 00000000: ff ff ff ff ff ff 00 0c 42 91 13 ab 08 00        ........B.....
[ 1822.368122] rose_route : unknown neighbour or device *
[ 1822.369566] rose_route : unknown neighbour or device *

It shows that rose_route_frame() is then correctly identifying a wrong neighbour and returns a 0 result, avoiding any dereference pointer. Consequently the kernel is then reporting a martian source.

Correcting the network wrong configuration by adding an IP address, a route and a gateway suppressed further martian source message.

I am just waiting for above code acceptation before I commit the patch.

Bernard, f6bvp