title: Reference count underflow in shiftfs
description: In shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu 5.0 and 5.3 kernel series, shiftfs_btrfs_ioctl_fd_replace() installs an fd referencing a file from the lower filesystem without taking an additional reference to that file. After the btrfs ioctl completes this fd is closed, which then puts a reference to that file, leading to a refcount underflow.
problem types: CWE-672 Operation on a Resource after Expiration or Release
affected:
{
product: Shiftfs in the Linux kernel
vendor: Ubuntu
versions:
changes: [at: 5.3.0-22.24, status: unaffected], lessThan: 5.3 kernel*, status: affected, version: 5.3.0-11.12, versionType: custom
lessThan: 5.0.0-35.38, status: affected, version: 5.0 kernel, versionType: custom
}
metrics:
cvssV3_1: [
attackComplexity: LOW
attackVector: LOCAL
availabilityImpact: HIGH
baseScore: 7.1
baseSeverity: HIGH
confidentialityImpact: NONE
integrityImpact: HIGH
privilegesRequired: LOW
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
version: 3.1
]