UBUNTU-CVE-2021-47506: Use After Free

Q: Which systems are exposed to this issue?

The affected software list includes Ubuntu Linux kernel packages for the standard, AWS, Azure, GCP, and FIPS variants. The issue is in the kernel NFS server code (nfsd) and concerns delegation handling.

Q: What conditions are involved in triggering the flaw?

A delegation break must race with delegation setup after vfs_setlease has been called. The callback can place a delegation on del_recall_lru before the delegation is hashed, allowing it to be freed while still present on that list.

Q: How might an affected system behave?

Symptoms may appear later rather than at the time of the race. Reported effects include use-after-free and list-corruption warnings, commonly observed in the nfsd laundromat thread.

Published May 24, 2024

Updated

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 vfssetlease. A delegation break runs a callback which immediately (in nfsd4cbrecallprepare) adds the delegation to delrecalllru. If we then exit nfs4setdelegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from delrecalllru. 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 Software

120 affected componentsFixes available

ubuntu/linux-azure<4.15.0-1131.144~14.04.1

4.15.0-1131.144~14.04.1

ubuntu/linux*

ubuntu/linux-aws<4.4.0-1143.149

4.4.0-1143.149

ubuntu/linux-lts-xenial<4.4.0-268.302~14.04.1

4.4.0-268.302~14.04.1

ubuntu/linux<4.4.0-268.302

4.4.0-268.302

ubuntu/linux-aws<4.4.0-1181.196

4.4.0-1181.196

ubuntu/linux-aws-hwe<4.15.0-1120.128~16.04.1

4.15.0-1120.128~16.04.1

ubuntu/linux-azure<4.15.0-1131.144~16.04.1

4.15.0-1131.144~16.04.1

ubuntu/linux-gcp<4.15.0-1116.130~16.04.1

4.15.0-1116.130~16.04.1

ubuntu/linux-hwe<4.15.0-169.177~16.04.1

4.15.0-169.177~16.04.1

ubuntu/linux-kvm<4.4.0-1144.155

4.4.0-1144.155

ubuntu/linux-oracle<4.15.0-1087.95~16.04.1

4.15.0-1087.95~16.04.1

ubuntu/linux-hwe-edge*

ubuntu/linux-fips<4.4.0-1113.120

4.4.0-1113.120

ubuntu/linux-fips*

ubuntu/linux<4.15.0-169.177

4.15.0-169.177

ubuntu/linux-aws<4.15.0-1121.129

4.15.0-1121.129

ubuntu/linux-aws-5.4<5.4.0-1069.73~18.04.1

5.4.0-1069.73~18.04.1

ubuntu/linux-azure-4.15<4.15.0-1131.144

4.15.0-1131.144

ubuntu/linux-azure-5.4<5.4.0-1073.76~18.04.1

5.4.0-1073.76~18.04.1

ubuntu/linux-gcp-4.15<4.15.0-1116.130

4.15.0-1116.130

ubuntu/linux-gcp-5.4<5.4.0-1068.72~18.04.1

5.4.0-1068.72~18.04.1

ubuntu/linux-hwe-5.4<5.4.0-105.119~18.04.1

5.4.0-105.119~18.04.1

ubuntu/linux-ibm-5.4<5.4.0-1018.20~18.04.1

5.4.0-1018.20~18.04.1

ubuntu/linux-kvm<4.15.0-1107.109

4.15.0-1107.109

ubuntu/linux-oracle<4.15.0-1087.95

4.15.0-1087.95

ubuntu/linux-oracle-5.4<5.4.0-1067.72~18.04.1

5.4.0-1067.72~18.04.1

ubuntu/linux-raspi-5.4<5.4.0-1056.63~18.04.1

5.4.0-1056.63~18.04.1

ubuntu/linux-aws-5.0*

ubuntu/linux-aws-5.3*

ubuntu/linux-azure*

ubuntu/linux-azure-5.3*

ubuntu/linux-azure-edge*

ubuntu/linux-gcp*

ubuntu/linux-gcp-5.3*

ubuntu/linux-gke-4.15*

ubuntu/linux-gke-5.4*

ubuntu/linux-gkeop-5.4*

ubuntu/linux-hwe*

ubuntu/linux-hwe-edge*

ubuntu/linux-oem*

ubuntu/linux-oracle-5.0*

ubuntu/linux-oracle-5.3*

ubuntu/linux-aws-fips<4.15.0-2061.63

4.15.0-2061.63

ubuntu/linux-azure-fips<4.15.0-2043.47

4.15.0-2043.47

ubuntu/linux-fips<4.15.0-1078.87

4.15.0-1078.87

ubuntu/linux-gcp-fips<4.15.0-2026.28

4.15.0-2026.28

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux<5.4.0-105.119

5.4.0-105.119

ubuntu/linux-aws<5.4.0-1069.73

5.4.0-1069.73

ubuntu/linux-azure<5.4.0-1073.76

5.4.0-1073.76

ubuntu/linux-bluefield<5.4.0-1032.35

5.4.0-1032.35

ubuntu/linux-gcp<5.4.0-1068.72

5.4.0-1068.72

ubuntu/linux-gkeop<5.4.0-1037.38

5.4.0-1037.38

ubuntu/linux-ibm<5.4.0-1018.20

5.4.0-1018.20

ubuntu/linux-kvm<5.4.0-1059.62

5.4.0-1059.62

ubuntu/linux-oracle<5.4.0-1067.72

5.4.0-1067.72

ubuntu/linux-raspi<5.4.0-1056.63

5.4.0-1056.63

ubuntu/linux-aws-5.11*

ubuntu/linux-aws-5.13*

ubuntu/linux-aws-5.8*

ubuntu/linux-azure-5.11*

ubuntu/linux-azure-5.13*

ubuntu/linux-azure-5.8*

ubuntu/linux-azure-fde*

ubuntu/linux-gcp-5.11*

ubuntu/linux-gcp-5.13*

ubuntu/linux-gcp-5.8*

ubuntu/linux-gke*

ubuntu/linux-gke-5.15*

ubuntu/linux-hwe-5.11*

ubuntu/linux-hwe-5.13*

ubuntu/linux-hwe-5.8*

ubuntu/linux-intel-5.13*

ubuntu/linux-oem-5.10*

ubuntu/linux-oem-5.13*

ubuntu/linux-oem-5.6*

ubuntu/linux-oracle-5.11*

ubuntu/linux-oracle-5.13*

ubuntu/linux-oracle-5.8*

ubuntu/linux-raspi2*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.11*

ubuntu/linux-riscv-5.8*

ubuntu/linux-aws-fips<5.4.0-1069.73+fips2

5.4.0-1069.73+fips2

ubuntu/linux-azure-fips<5.4.0-1073.76+fips1

5.4.0-1073.76+fips1

ubuntu/linux-fips<5.4.0-1046.52

5.4.0-1046.52

ubuntu/linux-gcp-fips<5.4.0-1067.71~20.04.1

5.4.0-1067.71~20.04.1

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux-allwinner-5.19*

ubuntu/linux-aws-5.19*

ubuntu/linux-aws-6.2*

ubuntu/linux-azure-5.19*

ubuntu/linux-azure-6.2*

ubuntu/linux-azure-fde-5.19*

ubuntu/linux-azure-fde-6.2*

ubuntu/linux-gcp-5.19*

ubuntu/linux-gcp-6.2*

ubuntu/linux-hwe-5.19*

ubuntu/linux-hwe-6.2*

ubuntu/linux-intel-iot-realtime*

ubuntu/linux-lowlatency-hwe-5.19*

ubuntu/linux-lowlatency-hwe-6.2*

ubuntu/linux-nvidia-6.2*

ubuntu/linux-oem-5.17*

ubuntu/linux-oem-6.0*

ubuntu/linux-oem-6.1*

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.19*

ubuntu/linux-starfive-5.19*

ubuntu/linux-starfive-6.2*

ubuntu/linux-raspi-realtime*

ubuntu/linux-vmware*

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 4.15.0-1131.144~14.04.1
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 4.4.0-1143.149
Upgrade
Upgrade ubuntu/linux-lts-xenial to a version that resolves this vulnerability.
Fixed in 4.4.0-268.302~14.04.1
Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 4.4.0-268.302
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 4.4.0-1181.196
Upgrade
Upgrade ubuntu/linux-aws-hwe to a version that resolves this vulnerability.
Fixed in 4.15.0-1120.128~16.04.1
Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 4.15.0-1131.144~16.04.1
Upgrade
Upgrade ubuntu/linux-gcp to a version that resolves this vulnerability.
Fixed in 4.15.0-1116.130~16.04.1
Upgrade
Upgrade ubuntu/linux-hwe to a version that resolves this vulnerability.
Fixed in 4.15.0-169.177~16.04.1
Upgrade
Upgrade ubuntu/linux-kvm to a version that resolves this vulnerability.
Fixed in 4.4.0-1144.155
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 4.15.0-1087.95~16.04.1
Upgrade
Upgrade ubuntu/linux-fips to a version that resolves this vulnerability.
Fixed in 4.4.0-1113.120
Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 4.15.0-169.177
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 4.15.0-1121.129
Upgrade
Upgrade ubuntu/linux-aws-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1069.73~18.04.1
Upgrade
Upgrade ubuntu/linux-azure-4.15 to a version that resolves this vulnerability.
Fixed in 4.15.0-1131.144
Upgrade
Upgrade ubuntu/linux-azure-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1073.76~18.04.1
Upgrade
Upgrade ubuntu/linux-gcp-4.15 to a version that resolves this vulnerability.
Fixed in 4.15.0-1116.130
Upgrade
Upgrade ubuntu/linux-gcp-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1068.72~18.04.1
Upgrade
Upgrade ubuntu/linux-hwe-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-105.119~18.04.1
Upgrade
Upgrade ubuntu/linux-ibm-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1018.20~18.04.1
Upgrade
Upgrade ubuntu/linux-kvm to a version that resolves this vulnerability.
Fixed in 4.15.0-1107.109
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 4.15.0-1087.95
Upgrade
Upgrade ubuntu/linux-oracle-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1067.72~18.04.1
Upgrade
Upgrade ubuntu/linux-raspi-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1056.63~18.04.1
Upgrade
Upgrade ubuntu/linux-aws-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-2061.63
Upgrade
Upgrade ubuntu/linux-azure-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-2043.47
Upgrade
Upgrade ubuntu/linux-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-1078.87
Upgrade
Upgrade ubuntu/linux-gcp-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-2026.28
Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 5.4.0-105.119
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 5.4.0-1069.73
Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 5.4.0-1073.76
Upgrade
Upgrade ubuntu/linux-bluefield to a version that resolves this vulnerability.
Fixed in 5.4.0-1032.35
Upgrade
Upgrade ubuntu/linux-gcp to a version that resolves this vulnerability.
Fixed in 5.4.0-1068.72
Upgrade
Upgrade ubuntu/linux-gkeop to a version that resolves this vulnerability.
Fixed in 5.4.0-1037.38
Upgrade
Upgrade ubuntu/linux-ibm to a version that resolves this vulnerability.
Fixed in 5.4.0-1018.20
Upgrade
Upgrade ubuntu/linux-kvm to a version that resolves this vulnerability.
Fixed in 5.4.0-1059.62
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 5.4.0-1067.72
Upgrade
Upgrade ubuntu/linux-raspi to a version that resolves this vulnerability.
Fixed in 5.4.0-1056.63
Upgrade
Upgrade ubuntu/linux-aws-fips to a version that resolves this vulnerability.
Fixed in 5.4.0-1069.73+fips2
Upgrade
Upgrade ubuntu/linux-azure-fips to a version that resolves this vulnerability.
Fixed in 5.4.0-1073.76+fips1
Upgrade
Upgrade ubuntu/linux-fips to a version that resolves this vulnerability.
Fixed in 5.4.0-1046.52
Upgrade
Upgrade ubuntu/linux-gcp-fips to a version that resolves this vulnerability.
Fixed in 5.4.0-1067.71~20.04.1

Event History

May 24, 2024

CVE Published

via OSV·03:15 PM

Data Sourced

via OSV·03:15 PM

DescriptionSeverityAffected Software

Frequently Asked Questions

Which systems are exposed to this issue?

The affected software list includes Ubuntu Linux kernel packages for the standard, AWS, Azure, GCP, and FIPS variants. The issue is in the kernel NFS server code (nfsd) and concerns delegation handling.

What conditions are involved in triggering the flaw?

A delegation break must race with delegation setup after vfs_setlease has been called. The callback can place a delegation on del_recall_lru before the delegation is hashed, allowing it to be freed while still present on that list.

How might an affected system behave?

Symptoms may appear later rather than at the time of the race. Reported effects include use-after-free and list-corruption warnings, commonly observed in the nfsd laundromat thread.

UBUNTU-CVE-2021-47506: Use After Free

Affected Software

Remediation

Event History

Frequently Asked Questions

Which systems are exposed to this issue?

What conditions are involved in triggering the flaw?

How might an affected system behave?

Company

Resources

Contact

Frequently Asked Questions

Which systems are exposed to this issue?

What conditions are involved in triggering the flaw?

How might an affected system behave?