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amazonAmazonALAS-2021-1636
HistoryMay 20, 2021 - 3:51 p.m.

Medium: kernel

2021-05-2015:51:00
alas.aws.amazon.com
11

7.1 High

AI Score

Confidence

High

0.001 Low

EPSS

Percentile

33.0%

Issue Overview:

2024-03-13: CVE-2021-46905 was added to this advisory.

2024-03-13: CVE-2021-46904 was added to this advisory.

2024-03-13: CVE-2021-46915 was added to this advisory.

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 read access. (CVE-2020-29374)

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. (CVE-2021-23133)

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. (CVE-2021-29155)

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. (CVE-2021-31829)

In the Linux kernel, the following vulnerability has been resolved:

net: hso: fix null-ptr-deref during tty device unregistration

Multiple ttys try to claim the same the minor number causing a double
unregistration of the same device. The first unregistration succeeds
but the next one results in a null-ptr-deref.

The get_free_serial_index() function returns an available minor number
but doesn’t assign it immediately. The assignment is done by the caller
later. But before this assignment, calls to get_free_serial_index()
would return the same minor number.

Fix this by modifying get_free_serial_index to assign the minor number
immediately after one is found to be and rename it to obtain_minor()
to better reflect what it does. Similary, rename set_serial_by_index()
to release_minor() and modify it to free up the minor number of the
given hso_serial. Every obtain_minor() should have corresponding
release_minor() call. (CVE-2021-46904)

In the Linux kernel, the following vulnerability has been resolved:

net: hso: fix NULL-deref on disconnect regression

Commit 8a12f8836145 (“net: hso: fix null-ptr-deref during tty device
unregistration”) fixed the racy minor allocation reported by syzbot, but
introduced an unconditional NULL-pointer dereference on every disconnect
instead.

Specifically, the serial device table must no longer be accessed after
the minor has been released by hso_serial_tty_unregister(). (CVE-2021-46905)

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nft_limit: avoid possible divide error in nft_limit_init

div_u64() divides u64 by u32.

nft_limit_init() wants to divide u64 by u64, use the appropriate
math function (div64_u64)

divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8390 Comm: syz-executor188 Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:div_u64_rem include/linux/math64.h:28 [inline]
RIP: 0010:div_u64 include/linux/math64.h:127 [inline]
RIP: 0010:nft_limit_init+0x2a2/0x5e0 net/netfilter/nft_limit.c:85
Code: ef 4c 01 eb 41 0f 92 c7 48 89 de e8 38 a5 22 fa 4d 85 ff 0f 85 97 02 00 00 e8 ea 9e 22 fa 4c 0f af f3 45 89 ed 31 d2 4c 89 f0 <49> f7 f5 49 89 c6 e8 d3 9e 22 fa 48 8d 7d 48 48 b8 00 00 00 00 00
RSP: 0018:ffffc90009447198 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000200000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff875152e6 RDI: 0000000000000003
RBP: ffff888020f80908 R08: 0000200000000000 R09: 0000000000000000
R10: ffffffff875152d8 R11: 0000000000000000 R12: ffffc90009447270
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 000000000097a300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000200001c4 CR3: 0000000026a52000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
nf_tables_newexpr net/netfilter/nf_tables_api.c:2675 [inline]
nft_expr_init+0x145/0x2d0 net/netfilter/nf_tables_api.c:2713
nft_set_elem_expr_alloc+0x27/0x280 net/netfilter/nf_tables_api.c:5160
nf_tables_newset+0x1997/0x3150 net/netfilter/nf_tables_api.c:4321
nfnetlink_rcv_batch+0x85a/0x21b0 net/netfilter/nfnetlink.c:456
nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:580 [inline]
nfnetlink_rcv+0x3af/0x420 net/netfilter/nfnetlink.c:598
netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
sock_sendmsg_nosec net/socket.c:654 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:674
____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
___sys_sendmsg+0xf3/0x170 net/socket.c:2404
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2433
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae (CVE-2021-46915)

Affected Packages:

kernel

Note:

This advisory is applicable to Amazon Linux 2 (AL2) Core repository. Visit this FAQ section for the difference between AL2 Core and AL2 Extras advisories.

Issue Correction:
Run yum update kernel to update your system.

New Packages:

aarch64:  
    kernel-4.14.232-176.381.amzn2.aarch64  
    kernel-headers-4.14.232-176.381.amzn2.aarch64  
    kernel-debuginfo-common-aarch64-4.14.232-176.381.amzn2.aarch64  
    perf-4.14.232-176.381.amzn2.aarch64  
    perf-debuginfo-4.14.232-176.381.amzn2.aarch64  
    python-perf-4.14.232-176.381.amzn2.aarch64  
    python-perf-debuginfo-4.14.232-176.381.amzn2.aarch64  
    kernel-tools-4.14.232-176.381.amzn2.aarch64  
    kernel-tools-devel-4.14.232-176.381.amzn2.aarch64  
    kernel-tools-debuginfo-4.14.232-176.381.amzn2.aarch64  
    kernel-devel-4.14.232-176.381.amzn2.aarch64  
    kernel-debuginfo-4.14.232-176.381.amzn2.aarch64  
  
i686:  
    kernel-headers-4.14.232-176.381.amzn2.i686  
  
src:  
    kernel-4.14.232-176.381.amzn2.src  
  
x86_64:  
    kernel-4.14.232-176.381.amzn2.x86_64  
    kernel-headers-4.14.232-176.381.amzn2.x86_64  
    kernel-debuginfo-common-x86_64-4.14.232-176.381.amzn2.x86_64  
    perf-4.14.232-176.381.amzn2.x86_64  
    perf-debuginfo-4.14.232-176.381.amzn2.x86_64  
    python-perf-4.14.232-176.381.amzn2.x86_64  
    python-perf-debuginfo-4.14.232-176.381.amzn2.x86_64  
    kernel-tools-4.14.232-176.381.amzn2.x86_64  
    kernel-tools-devel-4.14.232-176.381.amzn2.x86_64  
    kernel-tools-debuginfo-4.14.232-176.381.amzn2.x86_64  
    kernel-devel-4.14.232-176.381.amzn2.x86_64  
    kernel-debuginfo-4.14.232-176.381.amzn2.x86_64  
    kernel-livepatch-4.14.232-176.381-1.0-0.amzn2.x86_64  

Additional References

Red Hat: CVE-2020-29374, CVE-2021-23133, CVE-2021-29155, CVE-2021-31829, CVE-2021-46904, CVE-2021-46905, CVE-2021-46915

Mitre: CVE-2020-29374, CVE-2021-23133, CVE-2021-29155, CVE-2021-31829, CVE-2021-46904, CVE-2021-46905, CVE-2021-46915