{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2026-43420", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2026-43420", "idYear": 2026, "status": "PUBLISHED", "publishedAt": "2026-05-08T14:21:55.717Z", "updatedAt": "2026-05-11T22:24:14.623Z", "importedAt": "2026-10-24T01:58:14.884Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "ceph: fix i_nlink underrun during async unlink", "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix i_nlink underrun during async unlink\n\nDuring async unlink, we drop the `i_nlink` counter before we receive\nthe completion (that will eventually update the `i_nlink`) because \"we\nassume that the unlink will succeed\". That is not a bad idea, but it\nraces against deletions by other clients (or against the completion of\nour own unlink) and can lead to an underrun which emits a WARNING like\nthis one:\n\n WARNING: CPU: 85 PID: 25093 at fs/inode.c:407 drop_nlink+0x50/0x68\n Modules linked in:\n CPU: 85 UID: 3221252029 PID: 25093 Comm: php-cgi8.1 Not tainted 6.14.11-cm4all1-ampere #655\n Hardware name: Supermicro ARS-110M-NR/R12SPD-A, BIOS 1.1b 10/17/2023\n pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)\n pc : drop_nlink+0x50/0x68\n lr : ceph_unlink+0x6c4/0x720\n sp : ffff80012173bc90\n x29: ffff80012173bc90 x28: ffff086d0a45aaf8 x27: ffff0871d0eb5680\n x26: ffff087f2a64a718 x25: 0000020000000180 x24: 0000000061c88647\n x23: 0000000000000002 x22: ffff07ff9236d800 x21: 0000000000001203\n x20: ffff07ff9237b000 x19: ffff088b8296afc0 x18: 00000000f3c93365\n x17: 0000000000070000 x16: ffff08faffcbdfe8 x15: ffff08faffcbdfec\n x14: 0000000000000000 x13: 45445f65645f3037 x12: 34385f6369706f74\n x11: 0000a2653104bb20 x10: ffffd85f26d73290 x9 : ffffd85f25664f94\n x8 : 00000000000000c0 x7 : 0000000000000000 x6 : 0000000000000002\n x5 : 0000000000000081 x4 : 0000000000000481 x3 : 0000000000000000\n x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff08727d3f91e8\n Call trace:\n drop_nlink+0x50/0x68 (P)\n vfs_unlink+0xb0/0x2e8\n do_unlinkat+0x204/0x288\n __arm64_sys_unlinkat+0x3c/0x80\n invoke_syscall.constprop.0+0x54/0xe8\n do_el0_svc+0xa4/0xc8\n el0_svc+0x18/0x58\n el0t_64_sync_handler+0x104/0x130\n el0t_64_sync+0x154/0x158\n\nIn ceph_unlink(), a call to ceph_mdsc_submit_request() submits the\nCEPH_MDS_OP_UNLINK to the MDS, but does not wait for completion.\n\nMeanwhile, between this call and the following drop_nlink() call, a\nworker thread may process a CEPH_CAP_OP_IMPORT, CEPH_CAP_OP_GRANT or\njust a CEPH_MSG_CLIENT_REPLY (the latter of which could be our own\ncompletion). These will lead to a set_nlink() call, updating the\n`i_nlink` counter to the value received from the MDS. If that new\n`i_nlink` value happens to be zero, it is illegal to decrement it\nfurther. But that is exactly what ceph_unlink() will do then.\n\nThe WARNING can be reproduced this way:\n\n1. Force async unlink; only the async code path is affected. Having\n no real clue about Ceph internals, I was unable to find out why the\n MDS wouldn't give me the \"Fxr\" capabilities, so I patched\n get_caps_for_async_unlink() to always succeed.\n\n (Note that the WARNING dump above was found on an unpatched kernel,\n without this kludge - this is not a theoretical bug.)\n\n2. Add a sleep call after ceph_mdsc_submit_request() so the unlink\n completion gets handled by a worker thread before drop_nlink() is\n called. This guarantees that the `i_nlink` is already zero before\n drop_nlink() runs.\n\nThe solution is to skip the counter decrement when it is already zero,\nbut doing so without a lock is still racy (TOCTOU). Since\nceph_fill_inode() and handle_cap_grant() both hold the\n`ceph_inode_info.i_ceph_lock` spinlock while set_nlink() runs, this\nseems like the proper lock to protect the `i_nlink` updates.\n\nI found prior art in NFS and SMB (using `inode.i_lock`) and AFS (using\n`afs_vnode.cb_lock`). All three have the zero check as well.", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "9b31e88ac5623d15c8bc46f69dfe1d3b43a8f67c" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "6d5fd8bb574bef039eb3b738e523870433a2aeb9" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "fcc477a6e8856c8a42b3c9e171724d8d6dfadd06" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "b3f5513141ecc6b277a8f7b7efe58a0cf9a5e859" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "aedd29386b23f3e1e6818943e11abfff2953732f" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "7db008e85a5d17b64bc5390b828bf457ae91a415" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "8975b85b0d45ca811ace6fac5907652f2310e5ac" }, { "version": "2ccb45462aeaf0831397b90d31d3d50a7704fa1f", "status": "affected", "versionType": "git", "lessThan": "ce0123cbb4a40a2f1bbb815f292b26e96088639f" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "5.7", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "5.7" }, { "version": "5.10.253", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.15.203", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.15.*" }, { "version": "6.1.167", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.1.*" }, { "version": "6.6.130", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.6.*" }, { "version": "6.12.78", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.12.*" }, { "version": "6.18.19", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.18.*" }, { "version": "6.19.9", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.19.*" }, { "version": "7.0", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }