ext4: limit length to bitmap_maxbytes - blocksize in punch_hole

Syzbot found an issue [1] in ext4_fallocate().
The C reproducer [2] calls fallocate(), passing size 0xffeffeff000ul,
and offset 0x1000000ul, which, when added together exceed the
bitmap_maxbytes for the inode. This triggers a BUG in
ext4_ind_remove_space(). According to the comments in this function
the 'end' parameter needs to be one block after the last block to be
removed. In the case when the BUG is triggered it points to the last
block. Modify the ext4_punch_hole() function and add constraint that
caps the length to satisfy the one before laster block requirement.

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



Fixes: a4bb6b64 ("ext4: enable "punch hole" functionality")
Reported-by:  <syzbot+7a806094edd5d07ba029@syzkaller.appspotmail.com>
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Link: https://lore.kernel.org/r/20220331200515.153214-1-tadeusz.struk@linaro.org


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org