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.
- 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
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.
Sources
Also known as AZL-100355, BELL-CVE-2026-89557, DEBIAN-CVE-2026-89557, GHSA-233m-c5r9-wq53, UBUNTU-CVE-2026-89557.