CVE-2026-72217: SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing

CVE-2026-72217: SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

SUNRPC: Bound-check xdr_buf_to_bvec() stores before writing

xdr_buf_to_bvec() writes a bio_vec into the caller's array before
testing whether that slot is in range, and the head branch performs
the store with no check at all. When the caller's budget is exactly
used up, the next store lands one element past the end of the array.
The overflow label returns count - 1, which masks the surplus store
but cannot undo it.

rq_bvec, the array passed by nfsd_vfs_write(), is allocated to
exactly rq_maxpages entries with no slack. The OOB store can land in
adjacent slab memory; the bv_len and bv_offset fields written there
are derived from client-supplied RPC payload sizes.

Move the in-range check ahead of the store in the head, page-loop,
and tail branches. With the check at the top of each sequence, count
is incremented only after a successful store, so the overflow label
can return count directly.

The Linux kernel CVE team has assigned CVE-2026-72217 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.6 with commit 2eb2b93581813b74c7174961126f6ec38eadb5a7 and fixed in 6.6.145 with commit 4a1148f2739d5089c3ca8ae2e9d1053e219ab5df
	Issue introduced in 6.6 with commit 2eb2b93581813b74c7174961126f6ec38eadb5a7 and fixed in 6.12.97 with commit 6029e711a818bf34d6c4b90cafee24f3afffa110
	Issue introduced in 6.6 with commit 2eb2b93581813b74c7174961126f6ec38eadb5a7 and fixed in 6.18.40 with commit 69e18135e2a004a79505451dbef07314ea16e1eb
	Issue introduced in 6.6 with commit 2eb2b93581813b74c7174961126f6ec38eadb5a7 and fixed in 7.1.5 with commit 98414b42530af65cb984ffc12685096a3b5e179a
	Issue introduced in 6.6 with commit 2eb2b93581813b74c7174961126f6ec38eadb5a7 and fixed in 7.2-rc1 with commit 42f5b80dda6b86e424054baf1475df686c403d5c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-72217
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/sunrpc/xdr.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/4a1148f2739d5089c3ca8ae2e9d1053e219ab5df
	https://git.kernel.org/stable/c/6029e711a818bf34d6c4b90cafee24f3afffa110
	https://git.kernel.org/stable/c/69e18135e2a004a79505451dbef07314ea16e1eb
	https://git.kernel.org/stable/c/98414b42530af65cb984ffc12685096a3b5e179a
	https://git.kernel.org/stable/c/42f5b80dda6b86e424054baf1475df686c403d5c