Vulnerability CVE-2021-47114
Published: 2024-03-15

Description:
In the Linux kernel, the following vulnerability has been resolved:

ocfs2: fix data corruption by fallocate

When fallocate punches holes out of inode size, if original isize is in
the middle of last cluster, then the part from isize to the end of the
cluster will be zeroed with buffer write, at that time isize is not yet
updated to match the new size, if writeback is kicked in, it will invoke
ocfs2_writepage()->block_write_full_page() where the pages out of inode
size will be dropped. That will cause file corruption. Fix this by
zero out eof blocks when extending the inode size.

Running the following command with qemu-image 4.2.1 can get a corrupted
coverted image file easily.

qemu-img convert -p -t none -T none -f qcow2 $qcow_image \
-O qcow2 -o compat=1.1 $qcow_image.conv

The usage of fallocate in qemu is like this, it first punches holes out
of inode size, then extend the inode size.

fallocate(11, FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE, 2276196352, 65536) = 0
fallocate(11, 0, 2276196352, 65536) = 0

v1: https://www.spinics.net/lists/linux-fsdevel/msg193999.html
v2: https://lore.kernel.org/linux-fsdevel/20210525093034.GB4112@quack2.suse.cz/T/

 References:
https://git.kernel.org/stable/c/624fa7baa3788dc9e57840ba5b94bc22b03cda57
https://git.kernel.org/stable/c/33e03adafb29eedae1bae9cdb50c1385279fcf65
https://git.kernel.org/stable/c/a1700479524bb9cb5e8ae720236a6fabd003acae
https://git.kernel.org/stable/c/cec4e857ffaa8c447f51cd8ab4e72350077b6770
https://git.kernel.org/stable/c/cc2edb99ea606a45182b5ea38cc8f4e583aa0774
https://git.kernel.org/stable/c/c8d5faee46242c3f33b8a71a4d7d52214785bfcc
https://git.kernel.org/stable/c/0a31dd6fd2f4e7db538fb6eb1f06973d81f8dd3b
https://git.kernel.org/stable/c/6bba4471f0cc1296fe3c2089b9e52442d3074b2e
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