linux-ext4 - [Bug 200933] Divide zero in __ext4_check_dir

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Message-ID: <bug-200933-13602-EON2iQpyuT@https.bugzilla.kernel.org/>
Date:   Mon, 27 Aug 2018 13:37:07 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...nel.org
Subject: [Bug 200933] Divide zero in __ext4_check_dir_entry

https://bugzilla.kernel.org/show_bug.cgi?id=200933

Theodore Tso (tytso@....edu) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tytso@....edu

--- Comment #2 from Theodore Tso (tytso@....edu) ---
Created attachment 278125
  --> https://bugzilla.kernel.org/attachment.cgi?id=278125&action=edit
Simplified crafted image

Here is a simplified crafted image.   Here is also a simplified reproducer:

mount poc-200933.img.simplified /mnt
rmdir /mnt/foo/bar

The bug is in the function which checks to see if an inline directory is empty;
it is relying on the i_size of the inline directory, and if that value is
larger than what is correct, we can either overrun the buffer, or as in this
case, trigger a division by zero error when we find that the size of the next
"directory entry" is zero.   (This didn't trigger a KASAN error because it was
still a legal part of the inode table block.)

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