CVE-2021-47506: nfsd: fix use-after-free due to delegation race
First published: Fri 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 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.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux kernel | <4.4.296 | |
| Linux kernel | >=4.5<4.9.294 | |
| Linux kernel | >=4.10<4.14.259 | |
| Linux kernel | >=4.15<4.19.222 | |
| Linux kernel | >=4.20<5.4.168 | |
| Linux kernel | >=5.5<5.10.85 | |
| Linux kernel | >=5.11<5.15.8 | |
| Linux kernel | =5.15-rc1 | |
| Linux kernel | =5.15-rc2 | |
| Linux kernel | =5.15-rc3 | |
| Linux kernel | =5.15-rc4 |
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Reference Links
- https://git.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebce
- https://git.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4
- https://git.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536ee
- https://git.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4
- https://git.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09
- https://git.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373
- https://git.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3
- https://git.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5
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.
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