A data leak flaw was found in the way XFS_IOC_ALLOCSP IOCTL in the XFS filesystem allowed for size increase of files with unaligned size. A local attacker could use this flaw to leak data on the XFS filesystem otherwise not accessible to them.
A data leak flaw was found in the way XFS_IOC_ALLOCSP IOCTL in the XFS filesystem allowed for size increase of files with unaligned size. A local attacker could use this flaw to leak data on the XFS filesystem otherwise not accessible to them.
This issue can be mitigated by ensuring xfs_alloc_file_space is not called with "0" as an argument.
This can be done with a SystemTap script (which resets "0" with XFS_BMAPI_PREALLOC), below are the steps:
1) Save the following script in a 'CVE-2021-4155.stp' file
---
probe module("xfs").function("xfs_alloc_file_space") {
if ($alloc_type == 0)
$alloc_type = 0x8; # XFS_BMAPI_PREALLOC
}
---
2) Install systemtap package and its dependencies
# yum install -y systemtap systemtap-runtime
# yum install -y kernel-devel kernel-debuginfo
3) Build the mitigation kernel module as root.
# stap -r `uname -r` -m cve_2021_4155.ko -g CVE-2021-4155.stp -p4
4) Load the mitigation module as root
# staprun -L cve_2021_4155.ko
What is SystemTap and how to use it?
https://access.redhat.com/solutions/5441
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