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Date:   Thu, 14 Jul 2022 10:40:09 -0700
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Cc:     tytso@....edu,
        syzbot+15cd994e273307bf5cfa@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: block range must be validated before use in
 ext4_mb_clear_bb()

On 7/14/22 09:59, Lukas Czerner wrote:
> 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().

That works for me. Once applied it will need to be ported to stable
kernels. I will take care of that. Thanks!

Tested-by: Tadeusz Struk <tadeusz.struk@...aro.org>

-- 
Thanks,
Tadeusz

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