CVE-2026-89557

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.