CVE-2026-89530: svcrdma: Reject inline replies that overflow the pull-up buffer

CVE-2026-89530: svcrdma: Reject inline replies that overflow the pull-up buffer

[Greg Kroah-Hartman]

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

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

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

svcrdma: Reject inline replies that overflow the pull-up buffer

An RPC-over-RDMA client can request a reply, such as an NFS READ
payload, without providing a Write list or a Reply chunk to carry
it. When such a reply needs more scatter/gather entries than the
device's Send Queue supports, svc_rdma_pull_up_needed() selects
pull-up and svc_rdma_pull_up_reply_msg() linearizes the whole
reply into sctxt->sc_xprt_buf. That buffer is only sc_max_req_size
bytes, while the reply on this path is bounded only by the client's
request, so svc_rdma_xb_linearize() copies past the end of the
buffer and corrupts adjacent slab memory. The oversized length is
then stored in sc_sges[0].length and posted, so the device also
reads beyond the mapped region.

The SGE-exhaustion branch is the only pull-up path that can exceed
the buffer: the threshold branch pulls up only replies smaller
than RPCRDMA_PULLUP_THRESH, and replies that fit the device's SGE
budget are sent directly without linearization. Make
svc_rdma_pull_up_needed() report -E2BIG when the reply it would
pull up cannot fit sc_max_req_size, and fail the request with
ERR_CHUNK as RFC 8166 Section 4.5.3 directs rather than dropping
the connection.

The helper no longer answers a simple yes/no question: it now
reports pull-up, no pull-up, or -E2BIG for a reply too large to
linearize. Rename svc_rdma_pull_up_needed() to
svc_rdma_check_pull_up() so its name no longer implies a boolean
predicate.

The Linux kernel CVE team has assigned CVE-2026-89530 to this issue.


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

	Issue introduced in 5.0 with commit e248aa7be86e8179f20ac0931774ecd746f3f5bf and fixed in 6.12.109 with commit fcd91b9957462d398792201c239dffaeff1cc8b2
	Issue introduced in 5.0 with commit e248aa7be86e8179f20ac0931774ecd746f3f5bf and fixed in 6.18.50 with commit 1949dd1576f7a8aa161b1330c6125df9d53046d5
	Issue introduced in 5.0 with commit e248aa7be86e8179f20ac0931774ecd746f3f5bf and fixed in 7.2.4 with commit 8ec60eb51fae37cd3d334ff26e4a7d6fb21ff7cf
	Issue introduced in 5.0 with commit e248aa7be86e8179f20ac0931774ecd746f3f5bf and fixed in 7.3-rc1 with commit 0fbe20dfe74b783d255bf389a6ea77aa25dc7860
	Issue introduced in 4.19.22 with commit 9b65b18f817d9ada2bf67351f24bdcce6789a0bb
	Issue introduced in 4.20.9 with commit d564356e1919d1178568c19af410cfc1a9076663

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-2026-89530
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/xprtrdma/svc_rdma_sendto.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/fcd91b9957462d398792201c239dffaeff1cc8b2
	https://git.kernel.org/stable/c/1949dd1576f7a8aa161b1330c6125df9d53046d5
	https://git.kernel.org/stable/c/8ec60eb51fae37cd3d334ff26e4a7d6fb21ff7cf
	https://git.kernel.org/stable/c/0fbe20dfe74b783d255bf389a6ea77aa25dc7860