Re: kernel BUG at net/core/skbuff.c:LINE! (2)

Xin Long
2018-01-19T18:03:00Z

On Sat, Jan 20, 2018 at 1:19 AM, Guillaume Nault <g.nault@alphalink.fr> wrote:
> On Tue, Jan 16, 2018 at 04:21:40PM +0800, Xin Long wrote:
>> ipv4 tunnels don't really set dev->hard_header_len properly,
>> we may should fix it in pppoe by using needed_headroom,
>> as what it doesn't in arp_create.
>>
> I'm a bit in doubt about which device needs to be fixed. Should ip_gre
> set ->hard_header_len? Or should pppoe take ->needed_headroom into
> account in skb_reserve()? I'd favor the later option too, but I haven't
> figured out the semantic of these fields precisely enough to justify
> this choice.
That's also why I haven't posted the patch yet.
(Sorry, I almost forgot this mail.)

>
>> @@ -860,16 +861,16 @@ static int pppoe_sendmsg(struct socket *sock,
>> struct msghdr *m,
>> if (total_len > (dev->mtu + dev->hard_header_len))
>> goto end;
>>
>> + rlen = LL_RESERVED_SPACE(dev) + dev->needed_tailroom;
>>
>> - skb = sock_wmalloc(sk, total_len + dev->hard_header_len + 32,
>> - 0, GFP_KERNEL);
>> + skb = sock_wmalloc(sk, total_len + rlen + 32, 0, GFP_KERNEL);
>> if (!skb) {
>> error = -ENOMEM;
>> goto end;
>> }
>>
>> /* Reserve space for headers. */
>> - skb_reserve(skb, dev->hard_header_len);
>> + skb_reserve(skb, rlen);
> Any reason why you include dev->needed_tailroom in skb_reserve()?
> BTW, we also have to fix __pppoe_xmit.
I noticed them right after I replied, and was about to correct when submitting
and after figuring out the difference between hard_header_len and
needed_headroom.

it's good if you wish to do this with the following patch :-)

>
> What about this patch?
>
>
> ---- >8 ----
> diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
> index 4e1da1645b15..42518af53332 100644
> --- a/drivers/net/ppp/pppoe.c
> +++ b/drivers/net/ppp/pppoe.c
> @@ -842,6 +842,7 @@ static int pppoe_sendmsg(struct socket *sock, struct msghdr *m,
> struct pppoe_hdr *ph;
> struct net_device *dev;
> char *start;
> + int hlen;
>
> lock_sock(sk);
> if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED)) {
> @@ -860,16 +861,16 @@ static int pppoe_sendmsg(struct socket *sock, struct msghdr *m,
> if (total_len > (dev->mtu + dev->hard_header_len))
> goto end;
>
> -
> - skb = sock_wmalloc(sk, total_len + dev->hard_header_len + 32,
> - 0, GFP_KERNEL);
> + hlen = LL_RESERVED_SPACE(dev);
> + skb = sock_wmalloc(sk, hlen + sizeof(struct pppoe_hdr) + total_len +
> + dev->needed_tailroom, 0, GFP_KERNEL);
> if (!skb) {
> error = -ENOMEM;
> goto end;
> }
>
> /* Reserve space for headers. */
> - skb_reserve(skb, dev->hard_header_len);
> + skb_reserve(skb, hlen);
> skb_reset_network_header(skb);
>
> skb->dev = dev;
> @@ -930,7 +931,7 @@ static int __pppoe_xmit(struct sock *sk, struct sk_buff *skb)
> /* Copy the data if there is no space for the header or if it's
> * read-only.
> */
> - if (skb_cow_head(skb, sizeof(*ph) + dev->hard_header_len))
> + if (skb_cow_head(skb, LL_RESERVED_SPACE(dev) + sizeof(*ph)))
> goto abort;
>
> __skb_push(skb, sizeof(*ph));