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Vulnerability · Published May 24, 2024 · Assigned by Linux

CVE-2021-47506nfsd: fix use-after-free due to delegation race

Critical 9.8

In plain English

A critical-severity security flaw in Linux from Linux. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 56% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.8%top 43.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix use-after-free due to delegation race A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru. Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread. I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12linux5.15.15-1DEBIAN-CVE-2021-47506
Debian:13linux5.15.15-1DEBIAN-CVE-2021-47506
Debian:14linux5.15.15-1DEBIAN-CVE-2021-47506
Ubuntu:22.04:LTSlinux-allwinner-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-aws-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-aws-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-azure-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-azure-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-azure-fde-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-azure-fde-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-gcp-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-gcp-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-hwe-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-hwe-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-intel-iot-realtimeno fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-lowlatency-hwe-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-lowlatency-hwe-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-nvidia-6.2no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-oem-5.17no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-oem-6.0no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-oem-6.1no fix listedUBUNTU-CVE-2021-47506
Ubuntu:24.04:LTSlinux-raspi-realtimeno fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-realtimeno fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-riscvno fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-riscv-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-starfive-5.19no fix listedUBUNTU-CVE-2021-47506
Ubuntu:22.04:LTSlinux-starfive-6.2no fix listedUBUNTU-CVE-2021-47506

Affected products (as reported)

VendorProductVersions
Linux Linux dff1399f8addf7129c49bb2227469da79cc30b47 – before 04a8d07f3d58308b92630045560799a3faa3ebcedff1399f8addf7129c49bb2227469da79cc30b47 – before 348714018139c39533c55661a0c7c990671396b4dff1399f8addf7129c49bb2227469da79cc30b47 – before 33645d3e22720cac1e4548f8fef57bf0649536eedff1399f8addf7129c49bb2227469da79cc30b47 – before 2becaa990b93cbd2928292c0b669d3abb6cf06d4dff1399f8addf7129c49bb2227469da79cc30b47 – before e0759696de6851d7536efddfdd2dfed4c4df1f09dff1399f8addf7129c49bb2227469da79cc30b47 – before eeb0711801f5e19ef654371b627682aed3b11373dff1399f8addf7129c49bb2227469da79cc30b47 – before 148c816f10fd11df27ca6a9b3238cdd42fa72cd3dff1399f8addf7129c49bb2227469da79cc30b47 – before 548ec0805c399c65ed66c6641be467f717833ab5
Linux Linux 3.17

References