[ALAS2-2021-1636] Amazon Linux 2 2017.12 - ALAS2-2021-1636: medium priority package update for kernel

Package updates are available for Amazon Linux 2 that fix the following vulnerabilities:
CVE-2021-31829:
A flaw was found in the Linux kernel's eBPF verification code. By default, accessing the eBPF verifier is only accessible to privileged users with CAP_SYS_ADMIN. This flaw allows a local user who can insert eBPF instructions, to use the eBPF verifier to abuse a spectre-like flaw and infer all system memory. The highest threat from this vulnerability is to confidentiality.
1957788: CVE-2021-31829 kernel: protection of stack pointer against speculative pointer arithmetic can be bypassed to leak content of kernel memory

CVE-2021-29155:
A vulnerability was discovered in retrieve_ptr_limit in kernel/bpf/verifier.c in the Linux kernel mechanism to mitigate speculatively out-of-bounds loads (Spectre mitigation). In this flaw a local,
special user privileged (CAP_SYS_ADMIN) BPF program running on affected systems may bypass the protection, and execute speculatively out-of-bounds loads from the kernel memory. This can be abused to extract contents of kernel memory via side-channel.
1951595: CVE-2021-29155 kernel: protection for sequences of pointer arithmetic operations against speculatively out-of-bounds loads can be bypassed to leak content of kernel memory

CVE-2021-23133:
A use-after-free flaw was found in the Linux kernel's SCTP socket functionality that triggers a race condition. This flaw allows a local user to escalate their privileges on the system. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.
1948772: CVE-2021-23133 kernel: Race condition in sctp_destroy_sock list_del

CVE-2020-29374:
An issue was discovered in the Linux kernel related to mm/gup.c and mm/huge_memory.c. The get_user_pages (aka gup) implementation, when used for a copy-on-write page, does not properly consider the semantics of read operations and therefore can grant unintended write access.
1903249: CVE-2020-29374 kernel: the get_user_pages implementation when used for a copy-on-write page does not properly consider the semantics of read operations and therefore can grant unintended write access