fkie_cve-2025-39770
Vulnerability from fkie_nvd
Published
2025-09-11 17:15
Modified
2025-09-15 15:22
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: net: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM When performing Generic Segmentation Offload (GSO) on an IPv6 packet that contains extension headers, the kernel incorrectly requests checksum offload if the egress device only advertises NETIF_F_IPV6_CSUM feature, which has a strict contract: it supports checksum offload only for plain TCP or UDP over IPv6 and explicitly does not support packets with extension headers. The current GSO logic violates this contract by failing to disable the feature for packets with extension headers, such as those used in GREoIPv6 tunnels. This violation results in the device being asked to perform an operation it cannot support, leading to a `skb_warn_bad_offload` warning and a collapse of network throughput. While device TSO/USO is correctly bypassed in favor of software GSO for these packets, the GSO stack must be explicitly told not to request checksum offload. Mask NETIF_F_IPV6_CSUM, NETIF_F_TSO6 and NETIF_F_GSO_UDP_L4 in gso_features_check if the IPv6 header contains extension headers to compute checksum in software. The exception is a BIG TCP extension, which, as stated in commit 68e068cabd2c6c53 ("net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets"): "The feature is only enabled on devices that support BIG TCP TSO. The header is only present for PF_PACKET taps like tcpdump, and not transmitted by physical devices." kernel log output (truncated): WARNING: CPU: 1 PID: 5273 at net/core/dev.c:3535 skb_warn_bad_offload+0x81/0x140 ... Call Trace: <TASK> skb_checksum_help+0x12a/0x1f0 validate_xmit_skb+0x1a3/0x2d0 validate_xmit_skb_list+0x4f/0x80 sch_direct_xmit+0x1a2/0x380 __dev_xmit_skb+0x242/0x670 __dev_queue_xmit+0x3fc/0x7f0 ip6_finish_output2+0x25e/0x5d0 ip6_finish_output+0x1fc/0x3f0 ip6_tnl_xmit+0x608/0xc00 [ip6_tunnel] ip6gre_tunnel_xmit+0x1c0/0x390 [ip6_gre] dev_hard_start_xmit+0x63/0x1c0 __dev_queue_xmit+0x6d0/0x7f0 ip6_finish_output2+0x214/0x5d0 ip6_finish_output+0x1fc/0x3f0 ip6_xmit+0x2ca/0x6f0 ip6_finish_output+0x1fc/0x3f0 ip6_xmit+0x2ca/0x6f0 inet6_csk_xmit+0xeb/0x150 __tcp_transmit_skb+0x555/0xa80 tcp_write_xmit+0x32a/0xe90 tcp_sendmsg_locked+0x437/0x1110 tcp_sendmsg+0x2f/0x50 ... skb linear: 00000000: e4 3d 1a 7d ec 30 e4 3d 1a 7e 5d 90 86 dd 60 0e skb linear: 00000010: 00 0a 1b 34 3c 40 20 11 00 00 00 00 00 00 00 00 skb linear: 00000020: 00 00 00 00 00 12 20 11 00 00 00 00 00 00 00 00 skb linear: 00000030: 00 00 00 00 00 11 2f 00 04 01 04 01 01 00 00 00 skb linear: 00000040: 86 dd 60 0e 00 0a 1b 00 06 40 20 23 00 00 00 00 skb linear: 00000050: 00 00 00 00 00 00 00 00 00 12 20 23 00 00 00 00 skb linear: 00000060: 00 00 00 00 00 00 00 00 00 11 bf 96 14 51 13 f9 skb linear: 00000070: ae 27 a0 a8 2b e3 80 18 00 40 5b 6f 00 00 01 01 skb linear: 00000080: 08 0a 42 d4 50 d5 4b 70 f8 1a
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/041e2f945f82fdbd6fff577b79c33469430297aa
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/2156d9e9f2e483c8c3906c0ea57ea312c1424235
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/794ddbb7b63b6828c75967b9bcd43b086716e7a1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/864e3396976ef41de6cc7bc366276bf4e084fff2
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a0478d7e888028f85fa7785ea838ce0ca09398e2
Impacted products
Vendor Product Version


To clipboard 

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM\n\nWhen performing Generic Segmentation Offload (GSO) on an IPv6 packet that\ncontains extension headers, the kernel incorrectly requests checksum offload\nif the egress device only advertises NETIF_F_IPV6_CSUM feature, which has\na strict contract: it supports checksum offload only for plain TCP or UDP\nover IPv6 and explicitly does not support packets with extension headers.\nThe current GSO logic violates this contract by failing to disable the feature\nfor packets with extension headers, such as those used in GREoIPv6 tunnels.\n\nThis violation results in the device being asked to perform an operation\nit cannot support, leading to a `skb_warn_bad_offload` warning and a collapse\nof network throughput. While device TSO/USO is correctly bypassed in favor\nof software GSO for these packets, the GSO stack must be explicitly told not\nto request checksum offload.\n\nMask NETIF_F_IPV6_CSUM, NETIF_F_TSO6 and NETIF_F_GSO_UDP_L4\nin gso_features_check if the IPv6 header contains extension headers to compute\nchecksum in software.\n\nThe exception is a BIG TCP extension, which, as stated in commit\n68e068cabd2c6c53 (\"net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets\"):\n\"The feature is only enabled on devices that support BIG TCP TSO.\nThe header is only present for PF_PACKET taps like tcpdump,\nand not transmitted by physical devices.\"\n\nkernel log output (truncated):\nWARNING: CPU: 1 PID: 5273 at net/core/dev.c:3535 skb_warn_bad_offload+0x81/0x140\n...\nCall Trace:\n \u003cTASK\u003e\n skb_checksum_help+0x12a/0x1f0\n validate_xmit_skb+0x1a3/0x2d0\n validate_xmit_skb_list+0x4f/0x80\n sch_direct_xmit+0x1a2/0x380\n __dev_xmit_skb+0x242/0x670\n __dev_queue_xmit+0x3fc/0x7f0\n ip6_finish_output2+0x25e/0x5d0\n ip6_finish_output+0x1fc/0x3f0\n ip6_tnl_xmit+0x608/0xc00 [ip6_tunnel]\n ip6gre_tunnel_xmit+0x1c0/0x390 [ip6_gre]\n dev_hard_start_xmit+0x63/0x1c0\n __dev_queue_xmit+0x6d0/0x7f0\n ip6_finish_output2+0x214/0x5d0\n ip6_finish_output+0x1fc/0x3f0\n ip6_xmit+0x2ca/0x6f0\n ip6_finish_output+0x1fc/0x3f0\n ip6_xmit+0x2ca/0x6f0\n inet6_csk_xmit+0xeb/0x150\n __tcp_transmit_skb+0x555/0xa80\n tcp_write_xmit+0x32a/0xe90\n tcp_sendmsg_locked+0x437/0x1110\n tcp_sendmsg+0x2f/0x50\n...\nskb linear:   00000000: e4 3d 1a 7d ec 30 e4 3d 1a 7e 5d 90 86 dd 60 0e\nskb linear:   00000010: 00 0a 1b 34 3c 40 20 11 00 00 00 00 00 00 00 00\nskb linear:   00000020: 00 00 00 00 00 12 20 11 00 00 00 00 00 00 00 00\nskb linear:   00000030: 00 00 00 00 00 11 2f 00 04 01 04 01 01 00 00 00\nskb linear:   00000040: 86 dd 60 0e 00 0a 1b 00 06 40 20 23 00 00 00 00\nskb linear:   00000050: 00 00 00 00 00 00 00 00 00 12 20 23 00 00 00 00\nskb linear:   00000060: 00 00 00 00 00 00 00 00 00 11 bf 96 14 51 13 f9\nskb linear:   00000070: ae 27 a0 a8 2b e3 80 18 00 40 5b 6f 00 00 01 01\nskb linear:   00000080: 08 0a 42 d4 50 d5 4b 70 f8 1a"
    }
  ],
  "id": "CVE-2025-39770",
  "lastModified": "2025-09-15T15:22:38.297",
  "metrics": {},
  "published": "2025-09-11T17:15:42.530",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/041e2f945f82fdbd6fff577b79c33469430297aa"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/2156d9e9f2e483c8c3906c0ea57ea312c1424235"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/794ddbb7b63b6828c75967b9bcd43b086716e7a1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/864e3396976ef41de6cc7bc366276bf4e084fff2"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a0478d7e888028f85fa7785ea838ce0ca09398e2"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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