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Message-ID: <661d93b4e3ec3_3010129482@willemb.c.googlers.com.notmuch>
Date: Mon, 15 Apr 2024 16:53:08 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: shiming.cheng@...iatek.com,
edumazet@...gle.com,
davem@...emloft.net,
kuba@...nel.org,
pabeni@...hat.com,
matthias.bgg@...il.com,
steffen.klassert@...unet.com
Cc: linux-kernel@...r.kernel.org,
netdev@...r.kernel.org,
shiming.cheng@...iatek.com,
Lena Wang <lena.wang@...iatek.com>
Subject: Re: [PATCH net] udp: fix segmentation crash for GRO packet without
fraglist
shiming.cheng@ wrote:
> From: Shiming Cheng <shiming.cheng@...iatek.com>
>
> A GRO packet without fraglist is crashed and backtrace is as below:
> [ 1100.812205][ C3] CPU: 3 PID: 0 Comm: swapper/3 Tainted:
> G W OE 6.6.17-android15-0-g380371ea9bf1 #1
> [ 1100.812317][ C3] __udp_gso_segment+0x298/0x4d4
> [ 1100.812335][ C3] __skb_gso_segment+0xc4/0x120
> [ 1100.812339][ C3] udp_rcv_segment+0x50/0x134
> [ 1100.812344][ C3] udp_queue_rcv_skb+0x74/0x114
> [ 1100.812348][ C3] udp_unicast_rcv_skb+0x94/0xac
> [ 1100.812358][ C3] udp_rcv+0x20/0x30
>
> The reason that the packet loses its fraglist is that in ingress bpf
> it makes a test pull with to make sure it can read packet headers
> via direct packet access: In bpf_progs/offload.c
> try_make_writable -> bpf_skb_pull_data -> pskb_may_pull ->
> __pskb_pull_tail This operation pull the data in fraglist into linear
> and set the fraglist to null.
What is the right behavior from BPF with regard to SKB_GSO_FRAGLIST
skbs?
Some, like SCTP, cannot be linearized ever, as the do not have a
single gso_size.
Should this BPF operation just fail?
>
> BPF needs to modify a proper length to do pull data. However kernel
> should also improve the flow to avoid crash from a bpf function call.
> As there is no split flow and app may not decode the merged UDP packet,
> we should drop the packet without fraglist in skb_segment_list here.
>
> Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.")
> Signed-off-by: Shiming Cheng <shiming.cheng@...iatek.com>
> Signed-off-by: Lena Wang <lena.wang@...iatek.com>
> ---
> net/core/skbuff.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index b99127712e67..f68f2679b086 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4504,6 +4504,9 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
> if (err)
> goto err_linearize;
>
> + if (!list_skb)
> + goto err_linearize;
> +
> skb_shinfo(skb)->frag_list = NULL;
In absense of plugging the issue in BPF, dropping here is the best
we can do indeed, I think.
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