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CVE-2024-42256

Status: ModifiedCritical (9.8)—
Severity9.8Critical · CVSS 3.1
Exploitation probability0.69 %higher than 52% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found

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

cifs: Fix server re-repick on subrequest retry

When a subrequest is marked for needing retry, netfs will call cifs_prepare_write() which will make cifs repick the server for the op before renegotiating credits; it then calls cifs_issue_write() which invokes smb2_async_writev() - which re-repicks the server.

If a different server is then selected, this causes the increment of server->in_flight to happen against one record and the decrement to happen against another, leading to misaccounting.

Fix this by just removing the repick code in smb2_async_writev(). As this is only called from netfslib-driven code, cifs_prepare_write() should always have been called first, and so server should never be NULL and the preparatory step is repeated in the event that we do a retry.

Read full descriptionShow less

The problem manifests as a warning looking something like:

Which may be triggered by a number of different xfstests running against an Azure server in multichannel mode. generic/249 seems the most repeatable, but generic/215, generic/249 and generic/308 may also show it.

Technical details traces, logs and code from the original report
 WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs]
 ...
 RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs]
 ...
  smb2_writev_callback+0x334/0x560 [cifs]
  cifs_demultiplex_thread+0x77a/0x11b0 [cifs]
  kthread+0x187/0x1d0
  ret_from_fork+0x34/0x60
  ret_from_fork_asm+0x1a/0x30

CVSS

Base score
9.8
Version
3.1
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days
0.69 %
Percentile among all scored CVEs
52
Score date
10/21/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

Linux — Linux Kernel

CWEs

References

Show 2 references

Raw JSON (NVD)

Show
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    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: Fix server re-repick on subrequest retry\n\nWhen a subrequest is marked for needing retry, netfs will call\ncifs_prepare_write() which will make cifs repick the server for the op\nbefore renegotiating credits; it then calls cifs_issue_write() which\ninvokes smb2_async_writev() - which re-repicks the server.\n\nIf a different server is then selected, this causes the increment of\nserver->in_flight to happen against one record and the decrement to happen\nagainst another, leading to misaccounting.\n\nFix this by just removing the repick code in smb2_async_writev().  As this\nis only called from netfslib-driven code, cifs_prepare_write() should\nalways have been called first, and so server should never be NULL and the\npreparatory step is repeated in the event that we do a retry.\n\nThe problem manifests as a warning looking something like:\n\n WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs]\n ...\n RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs]\n ...\n  smb2_writev_callback+0x334/0x560 [cifs]\n  cifs_demultiplex_thread+0x77a/0x11b0 [cifs]\n  kthread+0x187/0x1d0\n  ret_from_fork+0x34/0x60\n  ret_from_fork_asm+0x1a/0x30\n\nWhich may be triggered by a number of different xfstests running against an\nAzure server in multichannel mode.  generic/249 seems the most repeatable,\nbut generic/215, generic/249 and generic/308 may also show it."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: cifs: corrige la repetición del servidor en el reintento de subrequest Cuando se marca una subrequest para necesitar un reintento, netfs llamará a cifs_prepare_write(), lo que hará que cifs vuelva a seleccionar el servidor para la operación antes de renegociar los créditos; luego llama a cifs_issue_write(), que invoca a smb2_async_writev(), que vuelve a seleccionar el servidor. Si luego se selecciona un servidor diferente, esto hace que el incremento de server->in_flight ocurra en un registro y la disminución en otro, lo que lleva a una contabilidad errónea. Solucione este problema simplemente eliminando el código de repetición en smb2_async_writev(). Como esto solo se llama desde código controlado por netfslib, siempre se debería haber llamado primero a cifs_prepare_write(), por lo que el servidor nunca debería ser NULL y el paso preparatorio se repite en caso de que hagamos un reintento. El problema se manifiesta como una advertencia similar a: ADVERTENCIA: CPU: 4 PID: 72896 en fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] ... RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] ... smb2_writev_callback+0x334/0x560 [cifs] cifs_demultiplex_thread+0x77a/0x11b0 [cifs] kthread+0x187/0x1d0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Que puede ser activado por varios xfstests corriendo contra un Servidor Azure en modo multicanal. generic/249 parece el más repetible, pero generic/215, generic/249 y generic/308 también pueden mostrarlo."
    }
  ],
  "lastModified": "2026-08-04T11:19:42.590",
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}