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[34.86.84.73]) by smtp.gmail.com with ESMTPSA id i6-20020ac84f46000000b004367bb1a200sm5685908qtw.70.2024.04.15.13.53.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Apr 2024 13:53:09 -0700 (PDT) Date: Mon, 15 Apr 2024 16:53:08 -0400 From: Willem de Bruijn To: shiming.cheng@mediatek.com, edumazet@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, matthias.bgg@gmail.com, steffen.klassert@secunet.com Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, shiming.cheng@mediatek.com, Lena Wang Message-ID: <661d93b4e3ec3_3010129482@willemb.c.googlers.com.notmuch> In-Reply-To: <20240415150103.23316-1-shiming.cheng@mediatek.com> References: <20240415150103.23316-1-shiming.cheng@mediatek.com> Subject: Re: [PATCH net] udp: fix segmentation crash for GRO packet without fraglist Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit shiming.cheng@ wrote: > From: Shiming Cheng > > 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 > Signed-off-by: Lena Wang > --- > 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.