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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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