CVE-2026-89678
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix partial-write detection in nfsd_direct_write nfsd_direct_write() walks a list of write segments and, after each vfs_iocb_iter_write(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset: host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter); if (host_err < 0) return host_err; *cnt += host_err; if (host_err < segments[i].iter.count) break; /* partial write */ vfs_iocb_iter_write() runs the iter through ->write_iter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length: before write_iter: iter.count == original_len after write_iter: iter.count == original_len - host_err The condition then reduces to host_err < original_len - host_err, so the break fires only when less than half of the segment was written. Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->ki_pos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting *cnt to the NFS client. Snapshot the segment's byte count before the write and compare host_err against that snapshot so any short write breaks the loop.
View original CVE JSON
{
"id": "CVE-2026-89678",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-09-11T20:19:54.523",
"lastModified": "2026-10-19T09:18:06.113",
"vulnStatus": "Received",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix partial-write detection in nfsd_direct_write\n\nnfsd_direct_write() walks a list of write segments and, after each\nvfs_iocb_iter_write(), tries to detect a short write so the loop can\nstop before placing the next segment at a wrong file offset:\n\n host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter);\n if (host_err < 0)\n return host_err;\n *cnt += host_err;\n if (host_err < segments[i].iter.count)\n break;\t/* partial write */\n\nvfs_iocb_iter_write() runs the iter through ->write_iter(), which\nadvances the iter by the number of bytes written. By the time the\ncheck runs, segments[i].iter.count is the residual, not the original\nrequest length:\n\n before write_iter: iter.count == original_len\n after write_iter: iter.count == original_len - host_err\n\nThe condition then reduces to host_err < original_len - host_err, so\nthe break fires only when less than half of the segment was written.\nAny short write completing between 50% and 99% of the segment slips\nthrough; the loop advances to the next segment with kiocb->ki_pos\nonly bumped by the short amount, writing the next segment's payload\nat the wrong offset and over-reporting *cnt to the NFS client.\n\nSnapshot the segment's byte count before the write and compare\nhost_err against that snapshot so any short write breaks the loop."
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"fs/nfsd/vfs.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
"lessThan": "fa6590dfd16ab55f03b658b079072ace3504825e",
"versionType": "git",
"status": "affected"
},
{
"version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
"lessThan": "250ec14932d5cfe102f68a57892bb566eee7f83e",
"versionType": "git",
"status": "affected"
}
]
},
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"fs/nfsd/vfs.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "6.19",
"status": "affected"
},
{
"version": "0",
"lessThan": "6.19",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.2.4",
"lessThanOrEqual": "7.2.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.3",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {
"cvssMetricV31": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary",
"cvssData": {
"version": "3.1",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
"baseScore": 7.5,
"baseSeverity": "HIGH",
"attackVector": "NETWORK",
"attackComplexity": "LOW",
"privilegesRequired": "NONE",
"userInteraction": "NONE",
"scope": "UNCHANGED",
"confidentialityImpact": "NONE",
"integrityImpact": "HIGH",
"availabilityImpact": "NONE"
},
"exploitabilityScore": 3.9,
"impactScore": 3.6
}
]
},
"references": [
{
"url": "https://git.kernel.org/stable/c/250ec14932d5cfe102f68a57892bb566eee7f83e",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/fa6590dfd16ab55f03b658b079072ace3504825e",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
]
}