CVE-2023-52854 padata: Fix refcnt handling in padata_free_shell()

2024-05-2115:31:49

Linux

github.com

linux kernel

vulnerability

high-load arm64 environment

use-after-free

padata requirement

padata.c file

system load

softirq

refcount handling

7 High

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

10.4%

JSON

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

padata: Fix refcnt handling in padata_free_shell()

In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead
to system UAF (Use-After-Free) issues. Due to the lengthy analysis of
the pcrypt_aead01 function call, I’ll describe the problem scenario
using a simplified model:

Suppose there’s a user of padata named user_function that adheres to
the padata requirement of calling padata_free_shell after serial()
has been invoked, as demonstrated in the following code:

struct request {
    struct padata_priv padata;
    struct completion *done;
};

void parallel(struct padata_priv *padata) {
    do_something();
}

void serial(struct padata_priv *padata) {
    struct request *request = container_of(padata,
    				struct request,
				padata);
    complete(request-&gt;done);
}

void user_function() {
    DECLARE_COMPLETION(done)
    padata-&gt;parallel = parallel;
    padata-&gt;serial = serial;
    padata_do_parallel();
    wait_for_completion(&done);
    padata_free_shell();
}

In the corresponding padata.c file, there’s the following code:

static void padata_serial_worker(struct work_struct *serial_work) {
    ...
    cnt = 0;

    while (!list_empty(&local_list)) {
        ...
        padata-&gt;serial(padata);
        cnt++;
    }

    local_bh_enable();

    if (refcount_sub_and_test(cnt, &pd-&gt;refcnt))
        padata_free_pd(pd);
}

Because of the high system load and the accumulation of unexecuted
softirq at this moment, local_bh_enable() in padata takes longer
to execute than usual. Subsequently, when accessing pd->refcnt,
pd has already been released by padata_free_shell(), resulting
in a UAF issue with pd->refcnt.

The fix is straightforward: add refcount_dec_and_test before calling
padata_free_pd in padata_free_shell.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "kernel/padata.c"
    ],
    "versions": [
      {
        "version": "07928d9bfc81",
        "lessThan": "41aad9d69539",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "07928d9bfc81",
        "lessThan": "0dd34a7ad395",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "07928d9bfc81",
        "lessThan": "c7c26d0ef5d2",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "07928d9bfc81",
        "lessThan": "1e901bcb8af1",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "07928d9bfc81",
        "lessThan": "1734a79e9519",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "07928d9bfc81",
        "lessThan": "7ddc21e317b3",
        "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/padata.c"
    ],
    "versions": [
      {
        "version": "5.6",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.6",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.201",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.139",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.1.63",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.5.12",
        "lessThanOrEqual": "6.5.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.2",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.7",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]