linux-ext4 - BUG in ext4_ind_remove

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Date:   Thu, 24 Feb 2022 17:12:56 -0800
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>
Cc:     linux-ext4@...r.kernel.org
Subject: BUG in ext4_ind_remove_space

Hi,
Syzbot found an issue [1] in fallocate() that looks to me like a loss of precision.
The C reproducer [2] calls fallocate() and passes the size 0xffeffeff000ul, and
offset 0x1000000ul, which is then used to calculate the first_block and
stop_block using ext4_lblk_t type (u32). I think this gets the MSB of the size
truncated and leads to invalid calculations, and eventually his BUG() in
https://elixir.bootlin.com/linux/v5.16.11/source/fs/ext4/indirect.c#L1244
The issue can be reproduced on 5.17.0-rc5, but I don't think it's a new
regression. I spent some time debugging it, but could spot anything obvious.
Can someone have a look please.

[1] https://syzkaller.appspot.com/bug?id=b80bd9cf348aac724a4f4dff251800106d721331
[2] https://syzkaller.appspot.com/text?tag=ReproC&x=14ba0238700000

-- 
Thanks,
Tadeusz