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.