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().

Link: https://syzkaller.appspot.com/bug?id=5266d464285a03cee9dbfda7d2452a72c3c2ae7c
Reported-by: syzbot+15cd994e273307bf5cfa@syzkaller.appspotmail.com
Signed-off-by: NLukas Czerner <lczerner@redhat.com>
Cc: Tadeusz Struk <tadeusz.struk@linaro.org>
Tested-by: NTadeusz Struk <tadeusz.struk@linaro.org>
Link: https://lore.kernel.org/r/20220714165903.58260-1-lczerner@redhat.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>