Messages in this thread | | | From | Eric Dumazet <> | Date | Tue, 9 May 2023 16:31:26 +0200 | Subject | Re: [PATCH net, v3] net: nsh: Use correct mac_offset to unwind gso skb in nsh_gso_segment() |
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On Tue, May 9, 2023 at 3:55 PM Dong Chenchen <dongchenchen2@huawei.com> wrote: > > As the call trace shows, skb_panic was caused by wrong skb->mac_header > in nsh_gso_segment(): > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI > CPU: 3 PID: 2737 Comm: syz Not tainted 6.3.0-next-20230505 #1 > RIP: 0010:skb_panic+0xda/0xe0 > call Trace: > skb_push+0x91/0xa0 > nsh_gso_segment+0x4f3/0x570 > skb_mac_gso_segment+0x19e/0x270 > __skb_gso_segment+0x1e8/0x3c0 > validate_xmit_skb+0x452/0x890 > validate_xmit_skb_list+0x99/0xd0 > sch_direct_xmit+0x294/0x7c0 > __dev_queue_xmit+0x16f0/0x1d70 > packet_xmit+0x185/0x210 > packet_snd+0xc15/0x1170 > packet_sendmsg+0x7b/0xa0 > sock_sendmsg+0x14f/0x160 > > The root cause is: > nsh_gso_segment() use skb->network_header - nhoff to reset mac_header > in skb_gso_error_unwind() if inner-layer protocol gso fails. > However, skb->network_header may be reset by inner-layer protocol > gso function e.g. mpls_gso_segment. skb->mac_header reset by the > inaccurate network_header will be larger than skb headroom. > > nsh_gso_segment > nhoff = skb->network_header - skb->mac_header; > __skb_pull(skb,nsh_len) > skb_mac_gso_segment > mpls_gso_segment > skb_reset_network_header(skb);//skb->network_header+=nsh_len > return -EINVAL; > skb_gso_error_unwind > skb_push(skb, nsh_len); > skb->mac_header = skb->network_header - nhoff; > // skb->mac_header > skb->headroom, cause skb_push panic > > Use correct mac_offset to restore mac_header to fix it. > > Fixes: c411ed854584 ("nsh: add GSO support") > Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com> > > --- > v2: > - Use skb->mac_header not skb->network_header-nhoff for mac_offset. > > v3: > - 'net' is noted in the subject. > - arrange local variable following reverse xmas tree order > --- > net/nsh/nsh.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/nsh/nsh.c b/net/nsh/nsh.c > index e9ca007718b7..793e0bd94558 100644 > --- a/net/nsh/nsh.c > +++ b/net/nsh/nsh.c > @@ -77,6 +77,7 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb, > netdev_features_t features) > { > struct sk_buff *segs = ERR_PTR(-EINVAL); > + u16 mac_offset = skb->mac_header; > unsigned int nsh_len, mac_len; > __be16 proto; > int nhoff; > @@ -108,8 +109,7 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb, > segs = skb_mac_gso_segment(skb, features); > if (IS_ERR_OR_NULL(segs)) { > skb_gso_error_unwind(skb, htons(ETH_P_NSH), nsh_len, > - skb->network_header - nhoff, > - mac_len); > + mac_offset, mac_len); > goto out; > } >
I do not think this patch is enough ?
This is still not nice, because mac_header == 0xFFFF
nhoff = skb->network_header - skb->mac_header; ... skb_set_mac_header(skb, -nhoff);
I would simply restore mac_header with "skb->mac_header = mac_offset" and get rid of nhoff.
(Accept the fact that GSO layer should not rely on skb mac_header being set)
In the future, we might be able to rewrite GSO without any assumptions on skb->mac_header.
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