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[34.85.235.172]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8144b049939sm70583417b3.32.2026.07.07.08.16.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2026 08:16:58 -0700 (PDT) Date: Tue, 07 Jul 2026 11:16:57 -0400 From: Willem de Bruijn To: Shiming Cheng , davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, matthias.bgg@gmail.com, angelogioacchino.delregno@collabora.com, willemb@google.com, daniel.zahka@gmail.com, alice@isovalent.com, sd@queasysnail.net, eilaimemedsnaimel@gmail.com, imv4bel@gmail.com, nbd@nbd.name, dsahern@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org Cc: stable@vger.kernel.org, steffen.klassert@secunet.com, lena.wang@mediatek.com, shiming.cheng@mediatek.com Message-ID: In-Reply-To: <20260707021425.483-1-shiming.cheng@mediatek.com> References: <20260707021425.483-1-shiming.cheng@mediatek.com> Subject: Re: [PATCH v6] net: gro: fix double aggregation of flush-marked skbs Precedence: bulk X-Mailing-List: stable@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: > The skb_gro_receive_list() function is missing a critical safety check > that exists in the skb_gro_receive() implementation. Specifically, it > does not validate NAPI_GRO_CB(skb)->flush before allowing packet > aggregation, as of commit 0ab03f353d36 ("net-gro: Fix GRO flush > when receiving a GSO packet."). It does not check .. as of commit .. ? No, skb_gro_receive checkos NAP_GRO_CB(skb)->flush as of that commit. > This allows already-GRO'd packets with existing frag_list to be > re-aggregated into a new GRO session, corrupting the frag_list chain > structure. When skb_segment() attempts to unpack these malformed packets, > it encounters invalid state and triggers a kernel panic. > > Scenario (Tethering/Device forwarding): > 1. Driver: Generated aggregated packet P1 via LRO with frag_list > 2. Dev A: Receives aggregated fraglist packet and flush flag set > 3. Dev A: Re-enters GRO, skb_gro_receive_list() is called > 4. Missing flush check allows re-aggregation despite flush flag > 5. Frag_list chain becomes corrupted (loops or dangling refs) > 6. Dev B: TX path calls skb_segment(), crashes on corrupted frag_list > > Root cause in skb_segment(): > The check at line ~4891: > if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) && > (skb_headlen(list_skb) == len || sg)) { > > When frag_list is corrupted by double aggregation, when list_skb is > a NULL pointer from skb->next, skb_headlen(list_skb) dereference > NULL/corrupted pointers occurs. > > Call Trace: > skb_headlen(NULL skb) > skb_segment > tcp_gso_segment > tcp4_gso_segment > inet_gso_segment > skb_mac_gso_segment > __skb_gso_segment > skb_gso_segment > validate_xmit_skb > validate_xmit_skb_list > sch_direct_xmit > qdisc_restart > __qdisc_run > qdisc_run > net_tx_action > > Fix: Add NAPI_GRO_CB(skb)->flush validation to the early-return check in > skb_gro_receive_list(), matching the defensive programming pattern of > skb_gro_receive(). > > Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.") > Cc: stable@vger.kernel.org > Signed-off-by: Shiming Cheng > --- > net/core/gro.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/net/core/gro.c b/net/core/gro.c > index 35f2f708f010..b413f4a6462b 100644 > --- a/net/core/gro.c > +++ b/net/core/gro.c > @@ -229,7 +229,9 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) > > int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb) > { > - if (unlikely(p->len + skb->len >= 65536)) > + /* make sure to check flush flag and to not merge */ > + if (unlikely(p->len + skb->len >= 65536 || > + NAPI_GRO_CB(skb)->flush)) > return -E2BIG; > > if (!pskb_may_pull(skb, skb_gro_offset(skb))) { > -- > 2.45.2 >