CVE-2020-16120 — Unprivileged overlay + shiftfs read access

Affected: Linux kernel

Overlayfs did not properly perform permission checking when copying up files in an overlayfs and could be exploited from within a user namespace, if, for example, unprivileged user namespaces were allowed. It was possible to have a file not readable by an unprivileged user to be copied to a mountpoint controlled by the user, like a removable device. This was introduced in kernel version 4.19 by commit d1d04ef ("ovl: stack file ops"). This was fixed in kernel version 5.8 by commits 56230d9 ("ovl: verify permissions in ovl_path_open()"), 48bd024 ("ovl: switch to mounter creds in readdir") and 05acefb ("ovl: check permission to open real file"). Additionally, commits 130fdbc ("ovl: pass correct flags for opening real directory") and 292f902 ("ovl: call secutiry hook in ovl_real_ioctl()") in kernel 5.8 might also be desired or necessary. These additional commits introduced a regression in overlay mounts within user namespaces which prevented access to files with ownership outside of the user namespace. This regression was mitigated by subsequent commit b6650da ("ovl: do not fail because of O_NOATIMEi") in kernel 5.11.

LSN-0072-1 — Kernel Live Patch Security Notice

Affected: Ubuntu:Pro:14.04:LTS: linux-lts-xenial, Ubuntu:Pro:16.04:LTS: linux-aws, Ubuntu:Pro:16.04:LTS: linux, Ubuntu:Pro:18.04:LTS: linux-aws, Ubuntu:Pro:18.04:LTS: linux, Ubuntu:Pro:18.04:LTS: linux-oem, Ubuntu:Pro:20.04:LTS: linux-aws, Ubuntu:Pro:20.04:LTS: linux-azure, Ubuntu:Pro:20.04:LTS: linux-gcp, Ubuntu:Pro:20.04:LTS: linux

It was discovered that the F2FS file system implementation in the Linux kernel did not properly perform bounds checking on xattrs in some situations. A local attacker could possibly use this to expose sensitive information (kernel memory). (CVE-2020-0067)

It was discovered that the Serial CAN interface driver in the Linux kernel did not properly initialize data. A local attacker could use this to expose sensitive information (kernel memory). (CVE-2020-11494)

Mauricio Faria de Oliveira discovered that the aufs implementation in the Linux kernel improperly managed inode reference counts in the vfsub_dentry_open() method. A local attacker could use this vulnerability to cause a denial of service. (CVE-2020-11935)

Piotr Krysiuk discovered that race conditions existed in the file system implementation in the Linux kernel. A local attacker could use this to cause a denial of service (system crash). (CVE-2020-12114)

Or Cohen discovered that the AF_PACKET implementation in the Linux kernel did not properly perform bounds checking in some situations. A local attacker could use this to cause a denial of service (system crash) or possibly execute arbitrary code. (CVE-2020-14386)

Hador Manor discovered that the DCCP protocol implementation in the Linux kernel improperly handled socket reuse, leading to a use-after-free vulnerability. A local attacker could use this to cause a denial of service (system crash) or possibly execute arbitrary code. (CVE-2020-16119)

Giuseppe Scrivano di…

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CVE-2020-16120 — Unprivileged overlay + shiftfs read access

LSN-0072-1 — Kernel Live Patch Security Notice