Describe CVE-2021-47179.
What is CVE-2021-47179?
In the Linux kernel, the following vulnerability has been resolved:

NFSv4: Fix a NULL pointer dereference in pnfs_mark_matching_lsegs_return()

Commit de144ff4234f changes _pnfs_return_layout() to call
pnfs_mark_matching_lsegs_return() passing NULL as the struct
pnfs_layout_range argument. Unfortunately,
pnfs_mark_matching_lsegs_return() doesn't check if we have a value here
before dereferencing it, causing an oops.

I'm able to hit this crash consistently when running connectathon basic
tests on NFS v4.1/v4.2 against Ontap..