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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5ec13f0fb63sm919521e0c.12.2026.10.22.18.29.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 18:29:43 -0700 (PDT) Date: Thu, 22 Oct 2026 21:29:42 -0400 From: Willem de Bruijn To: "Michael S. Tsirkin" , Eric Dumazet Cc: "David S . Miller" , Jakub Kicinski , Paolo Abeni , Willem de Bruijn , Simon Horman , netdev@vger.kernel.org, shaos , Jamal Hadi Salim Message-ID: In-Reply-To: <20261022120246-mutt-send-email-mst@kernel.org> References: <20261022155436.117507-1-edumazet@kernel.org> <20261022120246-mutt-send-email-mst@kernel.org> Subject: Re: [PATCH net] net: harden qdisc_pkt_len_segs_init() against malicious GSO packets X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Michael S. Tsirkin wrote: > On Thu, Oct 22, 2026 at 05:54:36PM +0200, Eric Dumazet wrote: > > An SKB_GSO_DODGY packet can carry untrusted gso_size and headers. > > > > For instance, gso_size=1 and hdr_len=65532 for a 524275-byte frame > > makes qdisc_pkt_len_segs_init() compute an accounted length of > > about 4,294,574,091 bytes (after gso_segs silently wrapped in a u16). > > > > With DRR quantum 256, the dequeue path then needs ~16.8 million > > deficit refills before it can dequeue the skb, keeping the CPU in > > the qdisc path long enough to trigger the soft-lockup watchdog. > > > > Commit 8f735d64382d ("net/sched: bound qdisc_pkt_len to prevent > > qdisc soft lockup") added QDISC_PKT_LEN_MAX to bound size table > > amplification. Use the same bound for DODGY packets: > > > > - Make gso_segs a u32 and drop packets whose segment count does > > not fit GSO_MAX_SEGS, instead of silently truncating it. > > > > - Drop packets whose estimated qdisc_pkt_len() would exceed > > QDISC_PKT_LEN_MAX. > > > > Fixes: 15e5a0307164 ("net_sched: better precise estimation on packet length for untrusted packets") > > Reported-by: shaos > > Closes: https://lore.kernel.org/netdev/20261022144755.65025-1-shawnq1@163.com/ > > Signed-off-by: Eric Dumazet > > Cc: Jamal Hadi Salim > > Cc: "Michael S. Tsirkin" > > I'm all for stack being more resilient. > > Acked-by: Michael S. Tsirkin Reviewed-by: Willem de Bruijn