Use After Free Affecting kernel-rt package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-rt package and not the kernel-rt package as distributed by Centos. See How to fix? for Centos:7 relevant fixed versions and status.

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.

• https://access.redhat.com/security/cve/CVE-2021-47506
• https://git.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebce
• https://git.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3
• https://git.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4
• https://git.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536ee
• https://git.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4
• https://git.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5
• https://git.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09
• https://git.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373