{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2024-42256", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-07-30T07:40:12.257Z", "datePublished": "2024-08-08T08:49:15.813Z", "dateUpdated": "2026-08-05T11:36:06.795Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T11:36:06.795Z" }, "descriptions": [ { "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." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - The trigger is the SMB write-retry path, and retries are dictated entirely by the remote SMB server's responses (`MID_REQUEST_SUBMITTED` on connection drop, or any `is_replayable_error()` status) reaching the client over TCP/445. A malicious/compromised server or an on-path attacker can force the retry at will.\nAC:L - The remote server can deterministically and repeatedly force write retries by returning replayable errors or dropping a channel's connection, and `cifs_pick_channel()` will select a different channel; there is no race or memory-layout condition outside the attacker's control.\nPR:N - The attacker is the remote SMB peer (or an on-path attacker) and needs no credentials or privileges on the victim client; the bug is hit during ordinary writeback on an already-established session.\nUI:N - The CIFS multichannel mount is a pre-existing environmental condition (fstab/autofs/cloud VM Azure Files mount), and at exploit time no victim action is required — ongoing background writeback is sufficient to enter the retry path.\nS:U - The credit and `in_flight` misaccounting is confined to the `TCP_Server_Info` structures of the client kernel's own CIFS session; no security boundary such as a VM or IOMMU domain is crossed.\nC:N - The defect is purely counter/credit misaccounting on the wrong channel record; tracing every use of `in_flight` and `server->credits` shows they index no memory and yield no read primitive or information disclosure.\nI:N - No memory is written out of bounds and no file data is altered — the write payload itself is transmitted correctly, only the per-channel credit and in-flight bookkeeping diverges.\nA:H - The bug reaches `WARN_ON_ONCE(server->in_flight == 0)` followed by an unsigned-integer underflow of `in_flight` to `UINT_MAX` (a kernel panic under `panic_on_warn`), and the permanently leaked credits on the original channel make `smb2_wait_mtu_credits()`'s untimed `wait_event_killable()` block forever, wedging the mount and stalling writeback indefinitely." } ] } ], "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": "3ee1a1fc39819906f04d6c62c180e760cd3a689d", "lessThan": "b1d0a566769b6fb3795b5289fc1daf9e0638d97a", "status": "affected", "versionType": "git" }, { "version": "3ee1a1fc39819906f04d6c62c180e760cd3a689d", "lessThan": "de40579b903883274fe203865f29d66b168b7236", "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": "semver" }, { "version": "6.10.1", "lessThanOrEqual": "6.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.11", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.10.1" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.11" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/b1d0a566769b6fb3795b5289fc1daf9e0638d97a" }, { "url": "https://git.kernel.org/stable/c/de40579b903883274fe203865f29d66b168b7236" } ], "title": "cifs: Fix server re-repick on subrequest retry", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2024-42256", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2024-09-10T16:12:59.830016Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2024-09-11T17:34:30.018Z" } } ] } }