CVE-2025-71090: nfsd: fix nfsd_file reference leak in nfsd4_add_rdaccess_to_wrdeleg()

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-01-13 · updated 2026-07-30

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix nfsd_file reference leak in nfsd4_add_rdaccess_to_wrdeleg() nfsd4_add_rdaccess_to_wrdeleg() unconditionally overwrites fp->fi_fds[O_RDONLY] with a newly acquired nfsd_file. However, if the client already has a SHARE_ACCESS_READ open from a previous OPEN operation, this action overwrites the existing pointer without releasing its reference, orphaning the previous reference. Additionally, the function originally stored the same nfsd_file pointer in both fp->fi_fds[O_RDONLY] and fp->fi_rdeleg_file with only a single reference. When put_deleg_file() runs, it clears fi_rdeleg_file and calls nfs4_file_put_access() to release the file. However, nfs4_file_put_access() only releases fi_fds[O_RDONLY] when the fi_access[O_RDONLY] counter drops to zero. If another READ open exists on the file, the counter remains elevated and the nfsd_file reference from the delegation is never released. This potentially causes open conflicts on that file. Then, on server shutdown, these leaks cause __nfsd_file_cache_purge() to encounter files with an elevated reference count that cannot be cleaned up, ultimately triggering a BUG() in kmem_cache_destroy() because there are still nfsd_file objects allocated in that cache.

Affected products

Linux kernel: from 6.17.1 before 6.18.4; 6.17, 6.19-rc1, 6.19-rc2, 6.19-rc3, 6.19-rc4, 6.19-rc5 (+3) — fixed in 6.18.4

How to fix

Upgrade to a fixed version: Linux kernel 6.18.4. Check the vendor advisory for mitigations.

References

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