GHSA-J9P8-CC5Q-CG54

Vulnerability from github – Published: 2025-10-07 18:31 – Updated: 2025-10-07 18:31
VLAI?
Details

In the Linux kernel, the following vulnerability has been resolved:

net: cdc_ncm: Deal with too low values of dwNtbOutMaxSize

Currently in cdc_ncm_check_tx_max(), if dwNtbOutMaxSize is lower than the calculated "min" value, but greater than zero, the logic sets tx_max to dwNtbOutMaxSize. This is then used to allocate a new SKB in cdc_ncm_fill_tx_frame() where all the data is handled.

For small values of dwNtbOutMaxSize the memory allocated during alloc_skb(dwNtbOutMaxSize, GFP_ATOMIC) will have the same size, due to how size is aligned at alloc time: size = SKB_DATA_ALIGN(size); size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); Thus we hit the same bug that we tried to squash with commit 2be6d4d16a084 ("net: cdc_ncm: Allow for dwNtbOutMaxSize to be unset or zero")

Low values of dwNtbOutMaxSize do not cause an issue presently because at alloc_skb() time more memory (512b) is allocated than required for the SKB headers alone (320b), leaving some space (512b - 320b = 192b) for CDC data (172b).

However, if more elements (for example 3 x u64 = [24b]) were added to one of the SKB header structs, say 'struct skb_shared_info', increasing its original size (320b [320b aligned]) to something larger (344b [384b aligned]), then suddenly the CDC data (172b) no longer fits in the spare SKB data area (512b - 384b = 128b).

Consequently the SKB bounds checking semantics fails and panics:

skbuff: skb_over_panic: text:ffffffff831f755b len:184 put:172 head:ffff88811f1c6c00 data:ffff88811f1c6c00 tail:0xb8 end:0x80 dev: ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:113! invalid opcode: 0000 [#1] PREEMPT SMP KASAN CPU: 0 PID: 57 Comm: kworker/0:2 Not tainted 5.15.106-syzkaller-00249-g19c0ed55a470 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023 Workqueue: mld mld_ifc_work RIP: 0010:skb_panic net/core/skbuff.c:113 [inline] RIP: 0010:skb_over_panic+0x14c/0x150 net/core/skbuff.c:118 [snip] Call Trace: skb_put+0x151/0x210 net/core/skbuff.c:2047 skb_put_zero include/linux/skbuff.h:2422 [inline] cdc_ncm_ndp16 drivers/net/usb/cdc_ncm.c:1131 [inline] cdc_ncm_fill_tx_frame+0x11ab/0x3da0 drivers/net/usb/cdc_ncm.c:1308 cdc_ncm_tx_fixup+0xa3/0x100

Deal with too low values of dwNtbOutMaxSize, clamp it in the range [USB_CDC_NCM_NTB_MIN_OUT_SIZE, CDC_NCM_NTB_MAX_SIZE_TX]. We ensure enough data space is allocated to handle CDC data by making sure dwNtbOutMaxSize is not smaller than USB_CDC_NCM_NTB_MIN_OUT_SIZE.

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{
  "affected": [],
  "aliases": [
    "CVE-2023-53667"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-10-07T16:15:50Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: cdc_ncm: Deal with too low values of dwNtbOutMaxSize\n\nCurrently in cdc_ncm_check_tx_max(), if dwNtbOutMaxSize is lower than\nthe calculated \"min\" value, but greater than zero, the logic sets\ntx_max to dwNtbOutMaxSize. This is then used to allocate a new SKB in\ncdc_ncm_fill_tx_frame() where all the data is handled.\n\nFor small values of dwNtbOutMaxSize the memory allocated during\nalloc_skb(dwNtbOutMaxSize, GFP_ATOMIC) will have the same size, due to\nhow size is aligned at alloc time:\n\tsize = SKB_DATA_ALIGN(size);\n        size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));\nThus we hit the same bug that we tried to squash with\ncommit 2be6d4d16a084 (\"net: cdc_ncm: Allow for dwNtbOutMaxSize to be unset or zero\")\n\nLow values of dwNtbOutMaxSize do not cause an issue presently because at\nalloc_skb() time more memory (512b) is allocated than required for the\nSKB headers alone (320b), leaving some space (512b - 320b = 192b)\nfor CDC data (172b).\n\nHowever, if more elements (for example 3 x u64 = [24b]) were added to\none of the SKB header structs, say \u0027struct skb_shared_info\u0027,\nincreasing its original size (320b [320b aligned]) to something larger\n(344b [384b aligned]), then suddenly the CDC data (172b) no longer\nfits in the spare SKB data area (512b - 384b = 128b).\n\nConsequently the SKB bounds checking semantics fails and panics:\n\nskbuff: skb_over_panic: text:ffffffff831f755b len:184 put:172 head:ffff88811f1c6c00 data:ffff88811f1c6c00 tail:0xb8 end:0x80 dev:\u003cNULL\u003e\n------------[ cut here ]------------\nkernel BUG at net/core/skbuff.c:113!\ninvalid opcode: 0000 [#1] PREEMPT SMP KASAN\nCPU: 0 PID: 57 Comm: kworker/0:2 Not tainted 5.15.106-syzkaller-00249-g19c0ed55a470 #0\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023\nWorkqueue: mld mld_ifc_work\nRIP: 0010:skb_panic net/core/skbuff.c:113 [inline]\nRIP: 0010:skb_over_panic+0x14c/0x150 net/core/skbuff.c:118\n[snip]\nCall Trace:\n \u003cTASK\u003e\n skb_put+0x151/0x210 net/core/skbuff.c:2047\n skb_put_zero include/linux/skbuff.h:2422 [inline]\n cdc_ncm_ndp16 drivers/net/usb/cdc_ncm.c:1131 [inline]\n cdc_ncm_fill_tx_frame+0x11ab/0x3da0 drivers/net/usb/cdc_ncm.c:1308\n cdc_ncm_tx_fixup+0xa3/0x100\n\nDeal with too low values of dwNtbOutMaxSize, clamp it in the range\n[USB_CDC_NCM_NTB_MIN_OUT_SIZE, CDC_NCM_NTB_MAX_SIZE_TX]. We ensure\nenough data space is allocated to handle CDC data by making sure\ndwNtbOutMaxSize is not smaller than USB_CDC_NCM_NTB_MIN_OUT_SIZE.",
  "id": "GHSA-j9p8-cc5q-cg54",
  "modified": "2025-10-07T18:31:10Z",
  "published": "2025-10-07T18:31:10Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-53667"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2334ff0b343ba6ba7a6c0586fcc83992bbbc1776"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/42b78c8cc774b47023d6d16d96d54cc7015e4a07"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6147745d43ff4e0d2c542e5b93e398ef0ee4db00"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/72d0240b0ee4794efc683975c213e4b384fea733"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7e01c7f7046efc2c7c192c3619db43292b98e997"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9be921854e983a81a0aeeae5febcd87093086e46"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/bf415bfe7573596ac213b4fd1da9e62cfc9a9413"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ff484163dfb61b58f23e4dbd007de1094427669c"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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