CVE-2024-42256

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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 \u2014 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 \u2014 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"}}]}}

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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["fs/smb/client/smb2pdu.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "b1d0a566769b6fb3795b5289fc1daf9e0638d97a", "status": "affected", "version": "3ee1a1fc39819906f04d6c62c180e760cd3a689d", "versionType": "git"}, {"lessThan": "de40579b903883274fe203865f29d66b168b7236", "status": "affected", "version": "3ee1a1fc39819906f04d6c62c180e760cd3a689d", "versionType": "git"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["fs/smb/client/smb2pdu.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "6.10"}, {"lessThan": "6.10", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "6.10.*", "status": "unaffected", "version": "6.10.1", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "6.11", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "CC5B6890-A2E7-41F8-AA56-E3202E9FB075", "versionEndExcluding": "6.10.1", "versionStartIncluding": "6.10", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "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."}, {"lang": "es", "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: cifs: corrige la repetici\u00f3n del servidor en el reintento de subrequest Cuando se marca una subrequest para necesitar un reintento, netfs llamar\u00e1 a cifs_prepare_write(), lo que har\u00e1 que cifs vuelva a seleccionar el servidor para la operaci\u00f3n antes de renegociar los cr\u00e9ditos; 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 disminuci\u00f3n en otro, lo que lleva a una contabilidad err\u00f3nea. Solucione este problema simplemente eliminando el c\u00f3digo de repetici\u00f3n en smb2_async_writev(). Como esto solo se llama desde c\u00f3digo controlado por netfslib, siempre se deber\u00eda haber llamado primero a cifs_prepare_write(), por lo que el servidor nunca deber\u00eda 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 m\u00e1s repetible, pero generic/215, generic/249 y generic/308 tambi\u00e9n pueden mostrarlo."}], "id": "CVE-2024-42256", "lastModified": "2026-08-04T11:19:42.590", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 9.8, "baseSeverity": "CRITICAL", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 5.9, "source": "nvd@nist.gov", "type": "Primary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2024-42256", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2024-09-10T16:12:59.830016Z", "version": "2.0.3"}}]}, "published": "2024-08-08T09:15:08.553", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/b1d0a566769b6fb3795b5289fc1daf9e0638d97a"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/de40579b903883274fe203865f29d66b168b7236"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "NVD-CWE-noinfo"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: cifs: Fix server re-repick on subrequest retry", "id": "2303637", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2303637"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.5", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "details": ["In the Linux kernel, the following vulnerability has been resolved:\ncifs: Fix server re-repick on subrequest retry\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.\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.\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.\nThe problem manifests as a warning looking something like:\nWARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs]\n...\nRIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs]\n...\nsmb2_writev_callback+0x334/0x560 [cifs]\ncifs_demultiplex_thread+0x77a/0x11b0 [cifs]\nkthread+0x187/0x1d0\nret_from_fork+0x34/0x60\nret_from_fork_asm+0x1a/0x30\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."], "name": "CVE-2024-42256", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2024-08-08T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2024-42256\nhttps://nvd.nist.gov/vuln/detail/CVE-2024-42256\nhttps://lore.kernel.org/linux-cve-announce/2024080820-CVE-2024-42256-afbb@gregkh/T"], "threat_severity": "Low"}

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