Incorrect calculation in Linux kernel - CVE-2020-29534

Vulnerability identifier: #VU93783

CSH Severity: Low

CVSS v4: 8.5 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2020-29534

CWE-ID: CWE-682

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to execute arbitrary code.

The vulnerability exists due to incorrect calculation within the __put_task_struct() and copy_process() functions in kernel/fork.c, within the __io_cqring_fill_event(), io_dismantle_req(), io_req_free_batch_finish(), io_req_free_batch(), io_close_prep(), io_req_drop_files(), io_req_set_file(), io_init_req(), io_submit_sqes(), io_sq_thread(), io_uring_alloc_task_context(), io_sq_offload_start(), io_wq_files_match(), io_uring_cancel_files(), io_cancel_task_cb(), SYSCALL_DEFINE6() and io_uring_get_fd() functions in fs/io_uring.c, within the exit_files() function in fs/file.c, within the bprm_execve() function in fs/exec.c. A local user can execute arbitrary code.

Linux kernel
Ubuntu
linux-image-5.8.0-34-generic-64k (Ubuntu package)
linux-image-5.8.0-34-generic (Ubuntu package)
linux-image-5.8.0-34-generic-lpae (Ubuntu package)
linux-image-5.8.0-34-lowlatency (Ubuntu package)
linux-image-virtual-hwe-20.04 (Ubuntu package)
linux-image-lowlatency-hwe-20.04 (Ubuntu package)
linux-image-generic-lpae-hwe-20.04 (Ubuntu package)
linux-image-generic-hwe-20.04 (Ubuntu package)
linux-image-generic (Ubuntu package)
linux-image-virtual (Ubuntu package)
linux-image-lowlatency (Ubuntu package)
linux-image-generic-lpae (Ubuntu package)
linux-image-generic-64k (Ubuntu package)
linux-image-5.8.0-1011-raspi (Ubuntu package)
linux-image-raspi (Ubuntu package)
linux-image-raspi-nolpae (Ubuntu package)
linux-image-5.8.0-1011-raspi-nolpae (Ubuntu package)
linux-image-oracle (Ubuntu package)
linux-image-5.8.0-1014-oracle (Ubuntu package)
linux-image-5.8.0-1014-kvm (Ubuntu package)
linux-image-kvm (Ubuntu package)
linux-image-gcp (Ubuntu package)
linux-image-gke (Ubuntu package)
linux-image-5.8.0-1015-gcp (Ubuntu package)
linux-image-azure (Ubuntu package)
linux-image-5.8.0-1016-azure (Ubuntu package)
linux-image-5.8.0-1017-aws (Ubuntu package)
linux-image-aws (Ubuntu package)

Install update from vendor's website.

linux-image-5.8.0-34-generic-64k (Ubuntu package) - update to 5.8.0-34.37
linux-image-5.8.0-34-generic (Ubuntu package) - update to 5.8.0-34.37~20.04.2
linux-image-5.8.0-34-generic-lpae (Ubuntu package) - update to 5.8.0-34.37~20.04.2
linux-image-5.8.0-34-lowlatency (Ubuntu package) - update to 5.8.0-34.37~20.04.2
linux-image-virtual-hwe-20.04 (Ubuntu package) - update to 5.8.0.34.37~20.04.20
linux-image-lowlatency-hwe-20.04 (Ubuntu package) - update to 5.8.0.34.37~20.04.20
linux-image-generic-lpae-hwe-20.04 (Ubuntu package) - update to 5.8.0.34.37~20.04.20
linux-image-generic-hwe-20.04 (Ubuntu package) - update to 5.8.0.34.37~20.04.20
linux-image-generic (Ubuntu package) - update to 5.8.0.34.39
linux-image-virtual (Ubuntu package) - update to 5.8.0.34.39
linux-image-lowlatency (Ubuntu package) - update to 5.8.0.34.39
linux-image-generic-lpae (Ubuntu package) - update to 5.8.0.34.39
linux-image-generic-64k (Ubuntu package) - update to 5.8.0.34.39
linux-image-5.8.0-1011-raspi (Ubuntu package) - update to 5.8.0-1011.14
linux-image-raspi (Ubuntu package) - update to 5.8.0.1011.14
linux-image-raspi-nolpae (Ubuntu package) - update to 5.8.0.1011.14
linux-image-5.8.0-1011-raspi-nolpae (Ubuntu package) - update to 5.8.0-1011.14
linux-image-oracle (Ubuntu package) - update to 5.8.0.1014.14
linux-image-5.8.0-1014-oracle (Ubuntu package) - update to 5.8.0-1014.14
linux-image-5.8.0-1014-kvm (Ubuntu package) - update to 5.8.0-1014.15
linux-image-kvm (Ubuntu package) - update to 5.8.0.1014.16
linux-image-gcp (Ubuntu package) - update to 5.8.0.1015.15
linux-image-gke (Ubuntu package) - update to 5.8.0.1015.15
linux-image-5.8.0-1015-gcp (Ubuntu package) - update to 5.8.0-1015.15
linux-image-azure (Ubuntu package) - update to 5.8.0.1016.16
linux-image-5.8.0-1016-azure (Ubuntu package) - update to 5.8.0-1016.17
linux-image-5.8.0-1017-aws (Ubuntu package) - update to 5.8.0-1017.18
linux-image-aws (Ubuntu package) - update to 5.8.0.1017.19

• https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0f2122045b946241a9e549c2a76cea54fa58a7ff
• https://bugs.chromium.org/p/project-zero/issues/detail?id=2089
• https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.9.3

• Incorrect calculation in Linux kernel fs
• Ubuntu update for linux