fs/ext4: fix integer overflow in s_log_groups_per_flex

syzbot found UBSAN: shift-out-of-bounds in ext4_mb_init [1], when
1 << sbi->s_es->s_log_groups_per_flex is bigger than UINT_MAX,
where sbi->s_mb_prefetch is unsigned integer type.

32 is the maximum allowed power of s_log_groups_per_flex. Following if
check will also trigger UBSAN shift-out-of-bound:

if (1 << sbi->s_es->s_log_groups_per_flex >= UINT_MAX) {

So I'm checking it against the raw number, perhaps there is another way
to calculate UINT_MAX max power. Also use min_t as to make sure it's
uint type.

[1] UBSAN: shift-out-of-bounds in fs/ext4/mballoc.c:2713:24
shift exponent 60 is too large for 32-bit type 'int'
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x137/0x1be lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:148 [inline]
 __ubsan_handle_shift_out_of_bounds+0x432/0x4d0 lib/ubsan.c:395
 ext4_mb_init_backend fs/ext4/mballoc.c:2713 [inline]
 ext4_mb_init+0x19bc/0x19f0 fs/ext4/mballoc.c:2898
 ext4_fill_super+0xc2ec/0xfbe0 fs/ext4/super.c:4983

Reported-by: [email protected]
Signed-off-by: Sabyrzhan Tasbolatov <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

0 files changed, 0 insertions, 0 deletions