Re: CVE-2026-97415: btrfs: tree-checker: validate names in ROOT_REF and ROOT_BACKREF

[Greg Kroah-Hartman <gregkh@kernel.org>]

On Wed, Sep 30, 2026 at 09:32:00AM +0200, Daniel Vacek wrote:
> Hi Greg,
> 
> > Description
> > ===========
> >
> > In the Linux kernel, the following vulnerability has been resolved:
> >
> > btrfs: tree-checker: validate names in ROOT_REF and ROOT_BACKREF
> >
> > ROOT_REF and ROOT_BACKREF items contain a struct btrfs_root_ref followed
> > by the subvolume name. Several readers assume that this layout is already
> > valid and then use the on-disk name length directly. A corrupted item can
> > therefore make those readers address bytes outside the item, and
> > BTRFS_IOC_GET_SUBVOL_INFO can copy too many bytes into its fixed-size UAPI
> > name buffer.
> >
> > Validate ROOT_REF and ROOT_BACKREF items in tree-checker before any reader
> > uses them. Reject records that do not contain a non-empty name, whose
> > name_len does not exactly describe the remaining item payload, or whose
> > name exceeds BTRFS_NAME_LEN.
> >
> > For BTRFS_IOC_GET_SUBVOL_INFO, copy only the validated on-disk name_len
> > instead of deriving the copy length from the item size. The ioctl result is
> > zeroed when allocated. That leaves the existing trailing zero byte
> > untouched.
> >
> > The Linux kernel CVE team has assigned CVE-2026-97415 to this issue.
> >
> >
> > Severity
> > ========
> >
> >   CVSS v3.1: 7.8 HIGH
> >   Vector:    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
> >
> >
> > Affected and fixed versions
> > ===========================
> >
> >         Issue introduced in 2.6.37 with commit 2ede0daf01549cecf4bb0962c46dc47382047523 and fixed in 6.12.111 with commit 9154542070ca7eadb3c764a882f39a127677854b
> >         Issue introduced in 2.6.37 with commit 2ede0daf01549cecf4bb0962c46dc47382047523 and fixed in 6.18.53 with commit 74f577c722c99248d804eca18e7de7c5e47549d7
> >         Issue introduced in 2.6.37 with commit 2ede0daf01549cecf4bb0962c46dc47382047523 and fixed in 7.2 with commit 0af37c217edf15fa21dac1c40822086df356c6bb
> 
> I believe this is inaccurate and the issue was in fact introduced in
> v4.18 with commit b64ec075bded2 ("btrfs: Add unprivileged ioctl which
> returns subvolume information")

Thanks for the review, I'll go fix up the record to reflect this.

greg k-h