CVE-2024-42256 cifs: Fix server re-repick on subrequest retry

2024-08-0808:49:15

Linux

www.cve.org

cve-2024-42256; cifs server re-repick; vulnerability fix; linux kernel; subrequest retry; netfs; cifs_prepare_write; smb2_async_writev; misaccounting; warning; smb2_add_credits; xfstests; azure server; multichannel mode; generic/249; generic/215; generic/308

EPSS

0.001

Percentile

36.3%

JSON

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.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "fs/smb/client/smb2pdu.c"
    ],
    "versions": [
      {
        "version": "3ee1a1fc3981",
        "lessThan": "b1d0a566769b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "3ee1a1fc3981",
        "lessThan": "de40579b9038",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "fs/smb/client/smb2pdu.c"
    ],
    "versions": [
      {
        "version": "6.10",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "6.10",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.10.1",
        "lessThanOrEqual": "6.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.11",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]