# CVE-2026-89557: md: do overflow check for sb->bblog_shift in super_1_load()

> An integer overflow in the Linux kernel's md driver allows a local attacker to cause a denial of service via a crafted superblock.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100355, BELL-CVE-2026-89557, DEBIAN-CVE-2026-89557, GHSA-233m-c5r9-wq53, UBUNTU-CVE-2026-89557

## What is CVE-2026-89557?

CVE-2026-89557 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

md: do overflow check for sb->bblog_shift in super_1_load()

In super_1_load(), sb->bblog_shift is an __u8 type value loaded from on-
disk superblock. It is used for badblocks API badblocks_set() by the
following sequence,

 1930   rdev->badblocks.shift = sb->bblog_shift;
 1931   for (i = 0 ; i < (sectors << (9-3)) ; i++, bbp++) {
 1932           u64 bb = le64_to_cpu(*bbp);
 1933           int count = bb & (0x3ff);
 1934           u64 sector = bb >> 10;
 1935           sector <<= sb->bblog_shift;
 1936           count <<= sb->bblog_shift;
 1937           if (bb + 1 == 0)
 1938                   break;
 1939           if (!badblocks_set(&rdev->badblocks, sector, count, 1))
 1940                   return -EINVAL;
 1941   }

bb->bblog_shit is in range of 0-255, variable sector is 64bit width, for
an invalid bb->bblog_shit, it is possible to make sector be overflowed
by the following calculation,
 1935           sector <<= sb->bblog_shift;
Then in turn when call badblocks_set() at line 1939 with the invalid
rdev->badblocks.shift set at line 1930, may result an overflow inside
_badblocks_clear() in block/badblocks.c.

Although there are many places to call badblocks APIs, the non-zero
shift value is only used in super_1_load(), other places always use 0 as
the shift value. Therefore it is unnecessary to do a general shift value
overflow check inside badblock API, and just check here as the caller.

This may avoid unnecessary check, make the badblocks API code more simple
and elegant.

## Which versions are affected by CVE-2026-89557?


## How do I fix CVE-2026-89557?

Apply the vendor's patch.

## Is CVE-2026-89557 being exploited?

There is no known exploitation of CVE-2026-89557 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89557 and fix it if it is affected.

What it is: CVE-2026-89557 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89557 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89557/ (Markdown: https://insights.sbomify.com/CVE-2026-89557/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89557
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89557
- OSV: https://osv.dev/vulnerability/CVE-2026-89557

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89557/
Summaries are generated and may contain mistakes; the official description above is the record.