CVE-2026-89557
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, the super_1_load() function in the md module did not validate the range of sb->bblog_shift loaded from the on-disk superblock. This value (0-255) is used as a bit shift when computing sector and block counts, which with an invalid value can overflow a 64-bit variable and cause an error in badblocks_set() in block/badblocks.c.
Risk Assessment
A malformed or crafted md array superblock can cause an overflow and kernel error, potentially leading to a system crash (panic) or other denial-of-service effects. Exploitation requires the ability to mount or process a malicious block device.
Recommendation
Update the Linux kernel to a version containing the fix that adds an overflow check for sb->bblog_shift in super_1_load(). Until then, avoid attaching untrusted block devices containing md arrays.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS