Re: [PATCH net] tipc: Check the bearer type before calling tipc_udp_nl_bearer_add()

[Shigeru Yoshida]

On Tue, 06 Feb 2024 08:53:14 +0100, Paolo Abeni wrote:
> On Thu, 2024-02-01 at 00:23 +0900, Shigeru Yoshida wrote:
>> syzbot reported the following general protection fault [1]:
>> 
>> general protection fault, probably for non-canonical address 0xdffffc0000000010: 0000 [#1] PREEMPT SMP KASAN
>> KASAN: null-ptr-deref in range [0x0000000000000080-0x0000000000000087]
>> ...
>> RIP: 0010:tipc_udp_is_known_peer+0x9c/0x250 net/tipc/udp_media.c:291
>> ...
>> Call Trace:
>>  <TASK>
>>  tipc_udp_nl_bearer_add+0x212/0x2f0 net/tipc/udp_media.c:646
>>  tipc_nl_bearer_add+0x21e/0x360 net/tipc/bearer.c:1089
>>  genl_family_rcv_msg_doit+0x1fc/0x2e0 net/netlink/genetlink.c:972
>>  genl_family_rcv_msg net/netlink/genetlink.c:1052 [inline]
>>  genl_rcv_msg+0x561/0x800 net/netlink/genetlink.c:1067
>>  netlink_rcv_skb+0x16b/0x440 net/netlink/af_netlink.c:2544
>>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1076
>>  netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]
>>  netlink_unicast+0x53b/0x810 net/netlink/af_netlink.c:1367
>>  netlink_sendmsg+0x8b7/0xd70 net/netlink/af_netlink.c:1909
>>  sock_sendmsg_nosec net/socket.c:730 [inline]
>>  __sock_sendmsg+0xd5/0x180 net/socket.c:745
>>  ____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
>>  ___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
>>  __sys_sendmsg+0x117/0x1e0 net/socket.c:2667
>>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
>>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> 
>> The cause of this issue is that when tipc_nl_bearer_add() is called with
>> the TIPC_NLA_BEARER_UDP_OPTS attribute, tipc_udp_nl_bearer_add() is called
>> even if the bearer is not UDP.
>> 
>> tipc_udp_is_known_peer() called by tipc_udp_nl_bearer_add() assumes that
>> the media_ptr field of the tipc_bearer has an udp_bearer type object, so
>> the function goes crazy for non-UDP bearers.
>> 
>> This patch fixes the issue by checking the bearer type before calling
>> tipc_udp_nl_bearer_add() in tipc_nl_bearer_add().
>> 
>> Fixes: ef20cd4dd163 ("tipc: introduce UDP replicast")
>> Reported-and-tested-by: syzbot+5142b87a9abc510e14fa@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Closes: https://syzkaller.appspot.com/bug?extid=5142b87a9abc510e14fa [1]
>> Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
>> ---
>>  net/tipc/bearer.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c
>> index 2cde375477e3..878415c43527 100644
>> --- a/net/tipc/bearer.c
>> +++ b/net/tipc/bearer.c
>> @@ -1086,6 +1086,12 @@ int tipc_nl_bearer_add(struct sk_buff *skb, struct genl_info *info)
>>  
>>  #ifdef CONFIG_TIPC_MEDIA_UDP
>>  	if (attrs[TIPC_NLA_BEARER_UDP_OPTS]) {
>> +		if (b->media->type_id != TIPC_MEDIA_TYPE_UDP) {
>> +			rtnl_unlock();
>> +			NL_SET_ERR_MSG(info->extack, "UDP option is unsupported");
>> +			return -EINVAL;
>> +		}
>> +
> 
> The patch LGTM, thanks!
> 
> As a side note, this function could probably deserve a net-next follow-
> up consolidation the error paths under a common label.

Thank you for commenting. I'll make a patch to clean up the error paths.

Thanks,
Shigeru

> 
> Cheers,
> 
> Paolo
>