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Wed, 16 Sep 2026 23:38:15 -0700 (PDT) Received: from localhost.localdomain ([183.194.144.114]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e35e532e4sm3211453a91.10.2026.09.16.23.38.12 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 16 Sep 2026 23:38:14 -0700 (PDT) From: zjamg To: mkl@pengutronix.de, mailhol@kernel.org, linux-can@vger.kernel.org Cc: socketcan@hartkopp.net, pabeni@redhat.com, linux-kernel@vger.kernel.org, zjamg , stable@vger.kernel.org Subject: [PATCH 1/1] can: restore skb header initialisations in init_can_skb() Date: Thu, 17 Sep 2026 14:37:44 +0800 Message-ID: <20260917063744.591-1-ndaugoing@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-can@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit 9f10374bb024 ("can: remove private CAN skb headroom infrastructure") removed the skb_reset_mac_header()/skb_reset_network_header()/ skb_reset_transport_header() calls from init_can_skb(). As a result, RX skbs from alloc_can_skb() and friends again carry mac_header = 0xFFFF. When such an skb reaches packet_rcv_spkt() (SOCK_PACKET), the push length calculation overflows and triggers skb_under_panic -> kernel BUG -> full machine panic. The same issue was originally reported in 2014 on linux-can and fixed by commit 969439016d2c ("can: add missing initialisations in CAN related skbuffs"). packet_rcv_spkt() itself has never been hardened: only packet_rcv() and tpacket_rcv() gained dev_has_header() checks in commit d549699048b4 ("net/packet: fix packet receive on L3 devices without visible hard header"). Fixes: 9f10374bb024 ("can: remove private CAN skb headroom infrastructure") Cc: stable@vger.kernel.org Signed-off-by: zjamg --- drivers/net/can/dev/skb.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/net/can/dev/skb.c b/drivers/net/can/dev/skb.c index 95fcdc1026f8..a0712e607b28 100644 --- a/drivers/net/can/dev/skb.c +++ b/drivers/net/can/dev/skb.c @@ -210,6 +210,14 @@ static void init_can_skb(struct sk_buff *skb) { skb->pkt_type = PACKET_BROADCAST; skb->ip_summed = CHECKSUM_UNNECESSARY; + + /* Restore the initialisations that were present before + * 9f10374bb024 to prevent skb_under_panic in packet_rcv_spkt + * and similar consumers. + */ + skb_reset_mac_header(skb); + skb_reset_network_header(skb); + skb_reset_transport_header(skb); } struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf) -- 2.53.0