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Date: Thu, 15 Dec 2022 09:29:05 -0800 From: Alexander H Duyck <alexander.duyck@...il.com> To: Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com>, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, shmulik@...anetworks.com, willemb@...gle.com, alexanderduyck@...com, netdev@...r.kernel.org, daniel@...earbox.net Cc: Sean Tranchetti <quic_stranche@...cinc.com> Subject: Re: [PATCH net v2] skbuff: Account for tail adjustment during pull operations On Wed, 2022-12-14 at 23:11 -0700, Subash Abhinov Kasiviswanathan wrote: > Extending the tail can have some unexpected side effects if a program uses > a helper like BPF_FUNC_skb_pull_data to read partial content beyond the > head skb headlen when all the skbs in the gso frag_list are linear with no > head_frag - > > kernel BUG at net/core/skbuff.c:4219! > pc : skb_segment+0xcf4/0xd2c > lr : skb_segment+0x63c/0xd2c > Call trace: > skb_segment+0xcf4/0xd2c > __udp_gso_segment+0xa4/0x544 > udp4_ufo_fragment+0x184/0x1c0 > inet_gso_segment+0x16c/0x3a4 > skb_mac_gso_segment+0xd4/0x1b0 > __skb_gso_segment+0xcc/0x12c > udp_rcv_segment+0x54/0x16c > udp_queue_rcv_skb+0x78/0x144 > udp_unicast_rcv_skb+0x8c/0xa4 > __udp4_lib_rcv+0x490/0x68c > udp_rcv+0x20/0x30 > ip_protocol_deliver_rcu+0x1b0/0x33c > ip_local_deliver+0xd8/0x1f0 > ip_rcv+0x98/0x1a4 > deliver_ptype_list_skb+0x98/0x1ec > __netif_receive_skb_core+0x978/0xc60 > > Fix this by marking these skbs as GSO_DODGY so segmentation can handle > the tail updates accordingly. > > Fixes: 3dcbdb134f32 ("net: gso: Fix skb_segment splat when splitting gso_size mangled skb having linear-headed frag_list") > Signed-off-by: Sean Tranchetti <quic_stranche@...cinc.com> > Signed-off-by: Subash Abhinov Kasiviswanathan <quic_subashab@...cinc.com> > --- > v2: Fix the issue in __pskb_pull_tail() instead of __bpf_try_make_writable() > as the issue is generic as mentioned by Daniel. Update the commit text > and Fixes tag accordingly. > > net/core/skbuff.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 88fa405..759bede 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -2416,6 +2416,9 @@ void *__pskb_pull_tail(struct sk_buff *skb, int delta) > insp = list; > } else { > /* Eaten partially. */ > + if (skb_is_gso(skb) && !list->head_frag && > + skb_headlen(list)) > + skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY; > > if (skb_shared(list)) { > /* Sucks! We need to fork list. :-( */ So essentially the effect here is that we are disabling scatter-gather when we segment this since we will have to allocate new buffers to realign the linear sections. Looks good to me. Reviewed-by: Alexander Duyck <alexanderduyck@...com>
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