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Date:   Fri, 5 May 2023 18:50:56 +0200
From:   Jan Kara <jack@suse.cz>
To:     Baokun Li <libaokun1@huawei.com>
Cc:     linux-ext4@vger.kernel.org, tytso@mit.edu,
        adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        yangerkun@huawei.com, yukuai3@huawei.com,
        syzbot+08106c4b7d60702dbc14@syzkaller.appspotmail.com
Subject: Re: [PATCH] ext4: check iomap type only if ext4_iomap_begin() does
 not fail
Message-ID: <20230505165056.7yjsh5nlaf4blvh5@quack3>
References: <20230505132429.714648-1-libaokun1@huawei.com>
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On Fri 05-05-23 21:24:29, Baokun Li wrote:
> When ext4_iomap_overwrite_begin() calls ext4_iomap_begin() map blocks may
> fail for some reason (e.g. memory allocation failure, bare disk write), and
> later because "iomap->type ! = IOMAP_MAPPED" triggers WARN_ON(). When ext4
> iomap_begin() returns an error, it is normal that the type of iomap->type
> may not match the expectation. Therefore, we only determine if iomap->type
> is as expected when ext4_iomap_begin() is executed successfully.
> 
> Reported-by: syzbot+08106c4b7d60702dbc14@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/all/00000000000015760b05f9b4eee9@google.com
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Makes sense. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0d5ba922e411..19c884abe52b 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3375,7 +3375,7 @@ static int ext4_iomap_overwrite_begin(struct inode *inode, loff_t offset,
>  	 */
>  	flags &= ~IOMAP_WRITE;
>  	ret = ext4_iomap_begin(inode, offset, length, flags, iomap, srcmap);
> -	WARN_ON_ONCE(iomap->type != IOMAP_MAPPED);
> +	WARN_ON_ONCE(!ret && iomap->type != IOMAP_MAPPED);
>  	return ret;
>  }
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR