Cleanup tipc_nl_bearer_add() error path

[yshigeru]

From Paolo Abeni:

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@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5142b87a9abc510e14fa [1]
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> ---
>  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.

Cheers,

Paolo

[yshigeru]

Sent v1 patch: https://lore.kernel.org/all/20240213134058.386123-1-syoshida@redhat.com/

[yshigeru]

Merged on net-next: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=984328c7657d