Bug 2401498 (CVE-2022-50487)

Summary:	CVE-2022-50487 kernel: NFSD: Protect against send buffer overflow in NFSv3 READDIR
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A buffer management flaw was found in the Linux kernel's NFS server implementation in the NFSv3 READDIR operation handling. A remote client can trigger this issue by crafting an RPC call with an oversized RPC record header, which forces the server to shrink its response buffer allocation. This causes the READDIR response construction to write beyond the available buffer space, resulting in a send buffer overflow that leads to memory corruption, denial of service via crash, or potential data integrity issues.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2025-10-04 16:04:04 UTC

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Protect against send buffer overflow in NFSv3 READDIR

Since before the git era, NFSD has conserved the number of pages
held by each nfsd thread by combining the RPC receive and send
buffers into a single array of pages. This works because there are
no cases where an operation needs a large RPC Call message and a
large RPC Reply message at the same time.

Once an RPC Call has been received, svc_process() updates
svc_rqst::rq_res to describe the part of rq_pages that can be
used for constructing the Reply. This means that the send buffer
(rq_res) shrinks when the received RPC record containing the RPC
Call is large.

A client can force this shrinkage on TCP by sending a correctly-
formed RPC Call header contained in an RPC record that is
excessively large. The full maximum payload size cannot be
constructed in that case.

Thanks to Aleksi Illikainen and Kari Hulkko for uncovering this
issue.

Comment 1 Alexander B 2025-10-06 15:20:00 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025100441-CVE-2022-50487-f5ea@gregkh/T