CVE-2021-47125 sch_htb: fix refcount leak in htb_parent_to_leaf_offload

2024-03-1520:14:30

Linux

github.com

linux kernel

refcount leak

htb_parent_to_leaf_offload

6.9 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

9.2%

JSON

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

sch_htb: fix refcount leak in htb_parent_to_leaf_offload

The commit ae81feb7338c (“sch_htb: fix null pointer dereference
on a null new_q”) fixes a NULL pointer dereference bug, but it
is not correct.

Because htb_graft_helper properly handles the case when new_q
is NULL, and after the previous patch by skipping this call
which creates an inconsistency : dev_queue->qdisc will still
point to the old qdisc, but cl->parent->leaf.q will point to
the new one (which will be noop_qdisc, because new_q was NULL).
The code is based on an assumption that these two pointers are
the same, so it can lead to refcount leaks.

The correct fix is to add a NULL pointer check to protect
qdisc_refcount_inc inside htb_parent_to_leaf_offload.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/sched/sch_htb.c"
    ],
    "versions": [
      {
        "version": "ae81feb7338c",
        "lessThan": "2411c02d0389",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ae81feb7338c",
        "lessThan": "944d671d5faa",
        "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/sched/sch_htb.c"
    ],
    "versions": [
      {
        "version": "5.12",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.12",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.12.10",
        "lessThanOrEqual": "5.12.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.13",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]