[ALAS2-2021-1704] Amazon Linux 2 2017.12 - ALAS2-2021-1704: medium priority package update for kernel

Package updates are available for Amazon Linux 2 that fix the following vulnerabilities:
CVE-2021-40490:
A flaw was found in the Linux kernel. A race condition was discovered in the ext4 subsystem. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
2001951: CVE-2021-40490 kernel: race condition was discovered in ext4_write_inline_data_end in fs/ext4/inline.c in the ext4 subsystem

CVE-2021-38198:
A flaw was found in the Linux kernel, where it incorrectly computes the access permissions of a shadow page. This issue leads to a missing guest protection page fault.
1992264: CVE-2021-38198 kernel: arch/x86/kvm/mmu/paging_tmpl.h incorrectly computes the access permissions of a shadow page

CVE-2021-3753:

Linux Kernel could allow a local attacker to obtain sensitive information, caused by an out-of-bounds read flaw in VT. By using a specially-crafted vc_visible_origin setting, an attacker could exploit this vulnerability to obtain sensitive information, or cause a denial of service condition.

CVE-2021-3732:
A flaw was found in the Linux kernel's OverlayFS subsystem in the way the user mounts the TmpFS filesystem with OverlayFS. This flaw allows a local user to gain access to hidden files that should not be accessible.
1995249: CVE-2021-3732 kernel: overlayfs: Mounting overlayfs inside an unprivileged user namespace can reveal files

CVE-2021-3656:
A flaw was found in the KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "virt_ext" field, this issue could allow a malicious L1 to disable both VMLOAD/VMSAVE intercepts and VLS (Virtual VMLOAD/VMSAVE) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape.
1983988: CVE-2021-3656 kernel: SVM nested virtualization issue in KVM (VMLOAD/VMSAVE)

CVE-2021-3653:
A flaw was found in the KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "int_ctl" field, this issue could allow a malicious L1 to enable AVIC support (Advanced Virtual Interrupt Controller) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape.
1983686: CVE-2021-3653 kernel: SVM nested virtualization issue in KVM (AVIC support)