CVE-2026-80789: nvmet-tcp: bound SGL data length before allocating command buffers

CVE-2026-80789: nvmet-tcp: bound SGL data length before allocating command buffers

[Greg Kroah-Hartman]

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

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

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

nvmet-tcp: bound SGL data length before allocating command buffers

nvmet_tcp_map_data() reads the host-controlled 32-bit sgl->length
and, for the in-capsule offset descriptor (type 0x01), checks it
against port->inline_data_size before use. Any other SGL descriptor
type -- including the non-inline transport SGL data-block descriptor
(type (NVME_TRANSPORT_SGL_DATA_DESC << 4) | NVME_SGL_FMT_TRANSPORT_A,
the type a real host uses for out-of-capsule writes) skips that check
entirely and falls straight through to:

	cmd->req.sg = sgl_alloc(len, GFP_KERNEL, &cmd->req.sg_cnt);

with len taken directly from the wire, unbounded up to 4 GiB.

nvmet_req_init() only parses the command and never inspects
sgl->length, and nvmet_check_transfer_len() -- the only other place
transfer_len is validated -- runs later, from req->execute(), after
the allocation has already happened. For a write command the target
responds with an R2T and parks the command waiting for the host to
send the data; if the host (or an unauthenticated peer that simply
never follows up) never does, the sgl_alloc() buffer stays resident
for the life of the command. NVMe/TCP has no mandatory authentication
in the default configuration, so any peer able to reach the target
portal and complete a Fabrics connect can drive this with a single
crafted command, repeatable across queues and connections for
amplification. This is unbounded kernel memory allocation
triggered by a remote, effectively unauthenticated peer.

Validate len against the same NVMET_TCP_MAXH2CDATA ceiling this file
already uses to bound per-PDU H2C data, for every SGL descriptor type,
before doing any allocation. This closes the gap for the non-inline
descriptor while leaving the existing, tighter inline_data_size check
in place for the in-capsule case.

Runtime-verified on a v6.19 KASAN stand: with this bound in place, a
crafted write command carrying an oversized non-inline SGL length is
rejected before sgl_alloc() runs, where the same request previously
drove an unbounded ~256 MiB kernel allocation (up to 4 GiB) that
stayed resident pending an R2T the host never satisfies.

The Linux kernel CVE team has assigned CVE-2026-80789 to this issue.


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

	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 5.10.269 with commit f6e51b09cbaa5f6f6e6a3a9dafa666f76c37aab5
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 5.15.220 with commit f63e89a0310264264923f84406dea05fe752de62
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 6.1.187 with commit 0952541b153e258b99d39cdb03ea6919fdeb41d0
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 6.6.156 with commit 25ad03d5c0e858c4b63f1e4b6d461d2af1b30b22
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 6.12.106 with commit d2acc96c528d589f5827cfb90e8e9229dd9d8cb4
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 6.18.47 with commit 6d27199ebe8cb223022150f74be13f154a964474
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 7.1.11 with commit 14dbe37681a6a7e346fc147bb363ec7cca3180a0
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 7.2.1 with commit d895e66628f939edbb98608f6e033d3d39e6e546
	Issue introduced in 5.0 with commit 872d26a391da92ed8f0c0f5cb5fef428067b7f30 and fixed in 7.3-rc1 with commit 4a3f00262a044e8e15064b1a6860968bf0500bf4

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-2026-80789
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:
	drivers/nvme/target/tcp.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/f6e51b09cbaa5f6f6e6a3a9dafa666f76c37aab5
	https://git.kernel.org/stable/c/f63e89a0310264264923f84406dea05fe752de62
	https://git.kernel.org/stable/c/0952541b153e258b99d39cdb03ea6919fdeb41d0
	https://git.kernel.org/stable/c/25ad03d5c0e858c4b63f1e4b6d461d2af1b30b22
	https://git.kernel.org/stable/c/d2acc96c528d589f5827cfb90e8e9229dd9d8cb4
	https://git.kernel.org/stable/c/6d27199ebe8cb223022150f74be13f154a964474
	https://git.kernel.org/stable/c/14dbe37681a6a7e346fc147bb363ec7cca3180a0
	https://git.kernel.org/stable/c/d895e66628f939edbb98608f6e033d3d39e6e546
	https://git.kernel.org/stable/c/4a3f00262a044e8e15064b1a6860968bf0500bf4