ext4: block range must be validated before use in ext4_mb_clear_bb()

In the Linux kernel, the following vulnerability has been resolved:

ext4: block range must be validated before use in ext4_mb_clear_bb()

Block range to free is validated in ext4_free_blocks() using

ext4_inode_block_valid() and then it's passed to ext4_mb_clear_bb().

However in some situations on bigalloc file system the range might be

adjusted after the validation in ext4_free_blocks() which can lead to

troubles on corrupted file systems such as one found by syzkaller that

resulted in the following BUG

kernel BUG at fs/ext4/ext4.h:3319!

PREEMPT SMP NOPTI

CPU: 28 PID: 4243 Comm: repro Kdump: loaded Not tainted 5.19.0-rc6+ #1

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014

RIP: 0010:ext4_free_blocks+0x95e/0xa90

Call Trace:

<TASK>

? lock_timer_base+0x61/0x80

? __es_remove_extent+0x5a/0x760

? __mod_timer+0x256/0x380

? ext4_ind_truncate_ensure_credits+0x90/0x220

ext4_clear_blocks+0x107/0x1b0

ext4_free_data+0x15b/0x170

ext4_ind_truncate+0x214/0x2c0

? _raw_spin_unlock+0x15/0x30

? ext4_discard_preallocations+0x15a/0x410

? ext4_journal_check_start+0xe/0x90

? __ext4_journal_start_sb+0x2f/0x110

ext4_truncate+0x1b5/0x460

? __ext4_journal_start_sb+0x2f/0x110

ext4_evict_inode+0x2b4/0x6f0

evict+0xd0/0x1d0

ext4_enable_quotas+0x11f/0x1f0

ext4_orphan_cleanup+0x3de/0x430

? proc_create_seq_private+0x43/0x50

ext4_fill_super+0x295f/0x3ae0

? snprintf+0x39/0x40

? sget_fc+0x19c/0x330

? ext4_reconfigure+0x850/0x850

get_tree_bdev+0x16d/0x260

vfs_get_tree+0x25/0xb0

path_mount+0x431/0xa70

__x64_sys_mount+0xe2/0x120

do_syscall_64+0x5b/0x80

? do_user_addr_fault+0x1e2/0x670

? exc_page_fault+0x70/0x170

entry_SYSCALL_64_after_hwframe+0x46/0xb0

RIP: 0033:0x7fdf4e512ace

Fix it by making sure that the block range is properly validated before

used every time it changes in ext4_free_blocks() or ext4_mb_clear_bb().