CVE-2021-47506: nfsd: fix use-after-free due to delegation race
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
Event History
Frequently Asked Questions
What is the severity of CVE-2021-47506?
CVE-2021-47506 is classified as a medium severity vulnerability in the Linux kernel due to the potential for use-after-free issues.
How do I fix CVE-2021-47506?
To fix CVE-2021-47506, update your Linux kernel to a version beyond the affected versions up to 5.15-rc4.
What versions of the Linux kernel are affected by CVE-2021-47506?
CVE-2021-47506 affects Linux kernel versions from 4.4.0 to 5.15-rc4.
What is the impact of CVE-2021-47506 on system security?
CVE-2021-47506 can lead to a use-after-free condition which may allow an attacker to execute arbitrary code in the kernel.
Is CVE-2021-47506 actively exploited in the wild?
As of now, there is no specific evidence indicating that CVE-2021-47506 is actively exploited in the wild.