// For flags

CVE-2024-42256

cifs: Fix server re-repick on subrequest retry

Severity Score

"-"
*CVSS v-

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

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.

The problem manifests as a warning looking something like:

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

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.

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.

*Credits: N/A
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* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-07-30 CVE Reserved
  • 2024-08-08 CVE Published
  • 2024-09-07 EPSS Updated
  • 2024-12-19 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 6.10 < 6.10.1
Search vendor "Linux" for product "Linux Kernel" and version " >= 6.10 < 6.10.1"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 6.10 < 6.11
Search vendor "Linux" for product "Linux Kernel" and version " >= 6.10 < 6.11"
en
Affected