CVE-2021-47506

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> nfsd: fix use-after-free due to delegation race<br /> <br /> A delegation break could arrive as soon as we&amp;#39;ve called vfs_setlease. A<br /> delegation break runs a callback which immediately (in<br /> nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we<br /> then exit nfs4_set_delegation without hashing the delegation, it will be<br /> freed as soon as the callback is done with it, without ever being<br /> removed from del_recall_lru.<br /> <br /> Symptoms show up later as use-after-free or list corruption warnings,<br /> usually in the laundromat thread.<br /> <br /> I suspect aba2072f4523 "nfsd: grant read delegations to clients holding<br /> writes" made this bug easier to hit, but I looked as far back as v3.0<br /> and it looks to me it already had the same problem. So I&amp;#39;m not sure<br /> where the bug was introduced; it may have been there from the beginning.