{"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"}}]}}