CVE-2021-47593 mptcp: clear 'kern' flag from fallback sockets

2024-06-1914:53:56

Linux

www.cve.org

mptcp

vulnerability

linux kernel

0.0004 Low

EPSS

Percentile

15.7%

JSON

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

mptcp: clear ‘kern’ flag from fallback sockets

The mptcp ULP extension relies on sk->sk_sock_kern being set correctly:
It prevents setsockopt(fd, IPPROTO_TCP, TCP_ULP, “mptcp”, 6); from
working for plain tcp sockets (any userspace-exposed socket).

But in case of fallback, accept() can return a plain tcp sk.
In such case, sk is still tagged as ‘kernel’ and setsockopt will work.

This will crash the kernel, The subflow extension has a NULL ctx->conn
mptcp socket:

BUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0
Call Trace:
tcp_data_ready+0xf8/0x370
[…]

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/mptcp/protocol.c"
    ],
    "versions": [
      {
        "version": "cf7da0d66cc1",
        "lessThan": "451f1eded7f5",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "cf7da0d66cc1",
        "lessThan": "c26ac0ea3a91",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "cf7da0d66cc1",
        "lessThan": "d6692b3b97bd",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/mptcp/protocol.c"
    ],
    "versions": [
      {
        "version": "5.6",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.6",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.88",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.11",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.16",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]