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CVE-2023-53667

Estado: AnalizadaMedia (5.5)—

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")

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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:

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.

Detalles técnicos trazas, registros y código del informe original
skbuff: skb_over_panic: text:ffffffff831f755b len:184 put:172 head:ffff88811f1c6c00 data:ffff88811f1c6c00 tail:0xb8 end:0x80 dev:<NULL>
------------[ 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:
 <TASK>
 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

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

CWE

Referencias

JSON original (NVD)

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          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
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      "value": "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 'struct skb_shared_info',\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:<NULL>\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 <TASK>\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."
    }
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  "lastModified": "2026-06-17T06:45:49.863",
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