CVE-2025-40212

*** Pendiente de traducción *** In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> nfsd: fix refcount leak in nfsd_set_fh_dentry()<br /> <br /> nfsd exports a "pseudo root filesystem" which is used by NFSv4 to find<br /> the various exported filesystems using LOOKUP requests from a known root<br /> filehandle. NFSv3 uses the MOUNT protocol to find those exported<br /> filesystems and so is not given access to the pseudo root filesystem.<br /> <br /> If a v3 (or v2) client uses a filehandle from that filesystem,<br /> nfsd_set_fh_dentry() will report an error, but still stores the export<br /> in "struct svc_fh" even though it also drops the reference (exp_put()).<br /> This means that when fh_put() is called an extra reference will be dropped<br /> which can lead to use-after-free and possible denial of service.<br /> <br /> Normal NFS usage will not provide a pseudo-root filehandle to a v3<br /> client. This bug can only be triggered by the client synthesising an<br /> incorrect filehandle.<br /> <br /> To fix this we move the assignments to the svc_fh later, after all<br /> possible error cases have been detected.