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.