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

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

[Daniel Vacek]

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")

--nX

> Please see https://www.kernel.org for a full list of currently supported
> kernel versions by the kernel community.
>
> Unaffected versions might change over time as fixes are backported to
> older supported kernel versions.  The official CVE entry at
>         https://cve.org/CVERecord/?id=CVE-2026-97415
> will be updated if fixes are backported, please check that for the most
> up to date information about this issue.
>
>
> Affected files
> ==============
>
> The file(s) affected by this issue are:
>         fs/btrfs/ioctl.c
>         fs/btrfs/tree-checker.c
>
>
> Mitigation
> ==========
>
> The Linux kernel CVE team recommends that you update to the latest
> stable kernel version for this, and many other bugfixes.  Individual
> changes are never tested alone, but rather are part of a larger kernel
> release.  Cherry-picking individual commits is not recommended or
> supported by the Linux kernel community at all.  If however, updating to
> the latest release is impossible, the individual changes to resolve this
> issue can be found at these commits:
>         https://git.kernel.org/stable/c/9154542070ca7eadb3c764a882f39a127677854b
>         https://git.kernel.org/stable/c/74f577c722c99248d804eca18e7de7c5e47549d7
>         https://git.kernel.org/stable/c/0af37c217edf15fa21dac1c40822086df356c6bb

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

[Greg Kroah-Hartman]

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