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SubjectRe: [PATCH] ext4: Fix i_disksize exceeding i_size problem in paritally written case
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Hi, Jan
> On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
>> Following process makes i_disksize exceed i_size:
>>
>> generic_perform_write
>> copied = iov_iter_copy_from_user_atomic(len) // copied < len
>> ext4_da_write_end
>> | ext4_update_i_disksize
>> | new_i_size = pos + copied;
>> | WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
>> | generic_write_end
>> | copied = block_write_end(copied, len) // copied = 0
>> | if (unlikely(copied < len))
>> | if (!PageUptodate(page))
>> | copied = 0;
>> | if (pos + copied > inode->i_size) // return false
>> if (unlikely(copied == 0))
>> goto again;
>> if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
>> status = -EFAULT;
>> break;
>> }
>>
>> We get i_disksize greater than i_size here, which could trigger WARNING
>> check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
>>
>> ext4_dio_write_iter
>> iomap_dio_rw
>> __iomap_dio_rw // return err, length is not aligned to 512
>> ext4_handle_inode_extension
>> WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
>>
>> WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
>> CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
>> RIP: 0010:ext4_file_write_iter+0xbc7
>> Call Trace:
>> vfs_write+0x3b1
>> ksys_write+0x77
>> do_syscall_64+0x39
>>
>> Fix it by putting block_write_end() before i_disksize updating just
>> like ext4_write_end() does.
>>
>> Fetch a reproducer in [Link].
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
>> Fixes: 64769240bd07f ("ext4: Add delayed allocation support in data=writeback mode")
>> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
>
> Good catch (although practically this will hardly have any negative
> effect). But rather than opencoding generic_write_end() I'd do:
>
> if (unlikely(copied < len) && !PageUptodate(page))
> copied = 0;
>
> at the beginning of ext4_da_write_end() and that should solve these
> problems as well?
>

Yes, your suggestion looks good, and I think we can put the checking
just after ext4_write_inline_data_end(Line 3150)? On the one hand, we
can pass original 'copied' value in trace_ext4_da_write_end(), one the
other hand, ext4_write_inline_data_end() already has this checking.

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