Amazon Linux AMI: CVE-2021-47506: Security patch for kernel (ALAS-2022-1563)

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.