A flaw was found in the QEMU disk image utility (qemu-img) 'info' command. A specially crafted image file containing a json:{} value describing block devices in QMP could cause the qemu-img process on the host to consume large amounts of memory or CPU time, leading to denial of service or read/write to an existing external file.

A flaw was found in the QEMU disk image utility (qemu-img) 'info' command. A specially crafted image file containing a json:{} value describing block devices in QMP could cause the qemu-img process on the host to consume large amounts of memory or CPU time, leading to denial of service, or read/write to an existing external file.

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 ocfs2writepage()->blockwritefullpage() 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 $qcowimage \ -O qcow2 -o compat=1.1 $qcowimage.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, FALLOCFLKEEPSIZE|FALLOCFLPUNCHHOLE, 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/