Re: [tipc-discussion] [net] tipc: fix NULL deref in tipc_link_xmit()

[Jon M. <jm...@re...>]

On 1/5/21 11:31 PM, Hoang Huu Le wrote:
> From: Hoang Le <hoa...@de...>
>
> The buffer list can have zero skb as following path:
> tipc_named_node_up()->tipc_node_xmit()->tipc_link_xmit(), so
> we need to check the list before casting an &sk_buff.
>
> Fault report:
>   [] tipc: Bulk publication failure
>   [] general protection fault, probably for non-canonical [#1] PREEMPT [...]
>   [] KASAN: null-ptr-deref in range [0x00000000000000c8-0x00000000000000cf]
>   [] CPU: 0 PID: 0 Comm: swapper/0 Kdump: loaded Not tainted 5.10.0-rc4+ #2
>   [] Hardware name: Bochs ..., BIOS Bochs 01/01/2011
>   [] RIP: 0010:tipc_link_xmit+0xc1/0x2180
>   [] Code: 24 b8 00 00 00 00 4d 39 ec 4c 0f 44 e8 e8 d7 0a 10 f9 48 [...]
>   [] RSP: 0018:ffffc90000006ea0 EFLAGS: 00010202
>   [] RAX: dffffc0000000000 RBX: ffff8880224da000 RCX: 1ffff11003d3cc0d
>   [] RDX: 0000000000000019 RSI: ffffffff886007b9 RDI: 00000000000000c8
>   [] RBP: ffffc90000007018 R08: 0000000000000001 R09: fffff52000000ded
>   [] R10: 0000000000000003 R11: fffff52000000dec R12: ffffc90000007148
>   [] R13: 0000000000000000 R14: 0000000000000000 R15: ffffc90000007018
>   [] FS:  0000000000000000(0000) GS:ffff888037400000(0000) knlGS:000[...]
>   [] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [] CR2: 00007fffd2db5000 CR3: 000000002b08f000 CR4: 00000000000006f0
>
> Signed-off-by: Hoang Le <hoa...@de...>
> ---
>   net/tipc/link.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/net/tipc/link.c b/net/tipc/link.c
> index 6ae2140eb4f7..a6a694b78927 100644
> --- a/net/tipc/link.c
> +++ b/net/tipc/link.c
> @@ -1030,7 +1030,6 @@ void tipc_link_reset(struct tipc_link *l)
>   int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
>   		   struct sk_buff_head *xmitq)
>   {
> -	struct tipc_msg *hdr = buf_msg(skb_peek(list));
>   	struct sk_buff_head *backlogq = &l->backlogq;
>   	struct sk_buff_head *transmq = &l->transmq;
>   	struct sk_buff *skb, *_skb;
> @@ -1038,13 +1037,18 @@ int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
>   	u16 ack = l->rcv_nxt - 1;
>   	u16 seqno = l->snd_nxt;
>   	int pkt_cnt = skb_queue_len(list);
> -	int imp = msg_importance(hdr);
>   	unsigned int mss = tipc_link_mss(l);
>   	unsigned int cwin = l->window;
>   	unsigned int mtu = l->mtu;
> +	struct tipc_msg *hdr;
>   	bool new_bundle;
>   	int rc = 0;
> +	int imp;
> +
> +	if (pkt_cnt <= 0)
> +		return 0;
>   
> +	hdr = buf_msg(skb_peek(list));
>   	if (unlikely(msg_size(hdr) > mtu)) {
>   		pr_warn("Too large msg, purging xmit list %d %d %d %d %d!\n",
>   			skb_queue_len(list), msg_user(hdr),
> @@ -1053,6 +1057,7 @@ int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
>   		return -EMSGSIZE;
>   	}
>   
> +	imp = msg_importance(hdr);
>   	/* Allow oversubscription of one data msg per source at congestion */
>   	if (unlikely(l->backlog[imp].len >= l->backlog[imp].limit)) {
>   		if (imp == TIPC_SYSTEM_IMPORTANCE) {
Acked-by: Jon Maloy <jm...@re...>