CVE-2021-47114 Information

Mar 16, 2024 cve

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/

Reference

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