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CVE-2022-49340

Estado: ModificadaMedia (5.5)—

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

ip_gre: test csum_start instead of transport header

GRE with TUNNEL_CSUM will apply local checksum offload on CHECKSUM_PARTIAL packets.

ipgre_xmit must validate csum_start after an optional skb_pull, else lco_csum may trigger an overflow. The original check was

This had false positives when skb_checksum_start is undefined: when ip_summed is not CHECKSUM_PARTIAL. A discussed refinement was straightforward

But was eventually revised more thoroughly: - restrict the check to the only branch where needed, in an uncommon GRE path that uses header_ops and calls skb_pull. - test skb_transport_header, which is set along with csum_start in skb_partial_csum_set in the normal header_ops datapath.

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Turns out skbs can arrive in this branch without the transport header set, e.g., through BPF redirection.

Revise the check back to check csum_start directly, and only if CHECKSUM_PARTIAL. Do leave the check in the updated location. Check field regardless of whether TUNNEL_CSUM is configured.

Detalles técnicos trazas, registros y código del informe original
	if (csum && skb_checksum_start(skb) < skb->data)
		return -EINVAL;

	if (csum && skb->ip_summed == CHECKSUM_PARTIAL &&
	    skb_checksum_start(skb) < skb->data)
		return -EINVAL;

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)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nip_gre: test csum_start instead of transport header\n\nGRE with TUNNEL_CSUM will apply local checksum offload on\nCHECKSUM_PARTIAL packets.\n\nipgre_xmit must validate csum_start after an optional skb_pull,\nelse lco_csum may trigger an overflow. The original check was\n\n\tif (csum && skb_checksum_start(skb) < skb->data)\n\t\treturn -EINVAL;\n\nThis had false positives when skb_checksum_start is undefined:\nwhen ip_summed is not CHECKSUM_PARTIAL. A discussed refinement\nwas straightforward\n\n\tif (csum && skb->ip_summed == CHECKSUM_PARTIAL &&\n\t    skb_checksum_start(skb) < skb->data)\n\t\treturn -EINVAL;\n\nBut was eventually revised more thoroughly:\n- restrict the check to the only branch where needed, in an\n  uncommon GRE path that uses header_ops and calls skb_pull.\n- test skb_transport_header, which is set along with csum_start\n  in skb_partial_csum_set in the normal header_ops datapath.\n\nTurns out skbs can arrive in this branch without the transport\nheader set, e.g., through BPF redirection.\n\nRevise the check back to check csum_start directly, and only if\nCHECKSUM_PARTIAL. Do leave the check in the updated location.\nCheck field regardless of whether TUNNEL_CSUM is configured."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: ip_gre: prueba csum_start en lugar del encabezado de transporte GRE con TUNNEL_CSUM aplicará la descarga de suma de comprobación local en los paquetes CHECKSUM_PARTIAL. ipgre_xmit debe validar csum_start después de un skb_pull opcional, de lo contrario lco_csum puede provocar un desbordamiento. La comprobación original era if (csum &amp;&amp; skb_checksum_start(skb) &lt; skb-&gt;data) return -EINVAL; Esto tenía falsos positivos cuando skb_checksum_start no está definido: cuando ip_summed no es CHECKSUM_PARTIAL. Una mejora discutida fue sencilla if (csum &amp;&amp; skb-&gt;ip_summed == CHECKSUM_PARTIAL &amp;&amp; skb_checksum_start(skb) &lt; skb-&gt;data) return -EINVAL; Pero finalmente se revisó más a fondo: - restringir la verificación a la única rama donde sea necesario, en una ruta GRE poco común que usa header_ops y llama a skb_pull. - probar skb_transport_header, que se establece junto con csum_start en skb_partial_csum_set en la ruta de datos header_ops normal. Resulta que skbs puede llegar a esta rama sin el encabezado de transporte establecido, por ejemplo, a través de la redirección BPF. Revise la verificación nuevamente para verificar csum_start directamente, y solo si CHECKSUM_PARTIAL. Deje la verificación en la ubicación actualizada. Verifique el campo independientemente de si TUNNEL_CSUM está configurado."
    }
  ],
  "lastModified": "2026-08-04T10:17:45.080",
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