CVE-2022-48921 sched/fair: Fix fault in reweight_entity

2024-08-2201:32:53

Linux

www.cve.org

linux kernel

sched/fair

reweight_entity

null pointer dereference

cfs

EPSS

Percentile

5.1%

JSON

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

sched/fair: Fix fault in reweight_entity

Syzbot found a GPF in reweight_entity. This has been bisected to
commit 4ef0c5c6b5ba (“kernel/sched: Fix sched_fork() access an invalid
sched_task_group”)

There is a race between sched_post_fork() and setpriority(PRIO_PGRP)
within a thread group that causes a null-ptr-deref in
reweight_entity() in CFS. The scenario is that the main process spawns
number of new threads, which then call setpriority(PRIO_PGRP, 0, -20),
wait, and exit. For each of the new threads the copy_process() gets
invoked, which adds the new task_struct and calls sched_post_fork()
for it.

In the above scenario there is a possibility that
setpriority(PRIO_PGRP) and set_one_prio() will be called for a thread
in the group that is just being created by copy_process(), and for
which the sched_post_fork() has not been executed yet. This will
trigger a null pointer dereference in reweight_entity(), as it will
try to access the run queue pointer, which hasn’t been set.

Before the mentioned change the cfs_rq pointer for the task has been
set in sched_fork(), which is called much earlier in copy_process(),
before the new task is added to the thread_group. Now it is done in
the sched_post_fork(), which is called after that. To fix the issue
the remove the update_load param from the update_load param() function
and call reweight_task() only if the task flag doesn’t have the
TASK_NEW flag set.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/sched/core.c"
    ],
    "versions": [
      {
        "version": "c85c6fadbef0",
        "lessThan": "8f317cd88805",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "3869eecf0504",
        "lessThan": "e0bcd6b57793",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "4ef0c5c6b5ba",
        "lessThan": "589a954daab5",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "4ef0c5c6b5ba",
        "lessThan": "13765de8148f",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/sched/core.c"
    ],
    "versions": [
      {
        "version": "5.16",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.16",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.137",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.27",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.16.13",
        "lessThanOrEqual": "5.16.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.17",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]