CVE-2026-74611: tls: rx: restore msg_iter before TLS 1.3 optimistic retry

From: Greg Kroah-Hartman <[email protected]>

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

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

tls: rx: restore msg_iter before TLS 1.3 optimistic retry

tls_decrypt_sg() advances msg->msg_iter when it maps user pages for
the optimistic TLS 1.3 zero-copy path. If the decrypted record turns
out not to be unpadded application data, tls_decrypt_sw() retries into
a kernel skb, but leaves the iterator advanced.

The subsequent copy from the skb then writes decrypted bytes again at
a later point in the caller iovecs while recvmsg() reports only the
post-retry length. A TLS peer can trigger this after the receiver
enables TLS_RX_EXPECT_NO_PAD.

Revert the iterator by the number of bytes consumed by the optimistic
mapping before retrying without zero-copy.

Add a selftest which sends a TLS 1.3 control record with
TLS_RX_EXPECT_NO_PAD enabled and verifies that recvmsg() does not
overwrite later iovecs beyond the returned length.

The Linux kernel CVE team has assigned CVE-2026-74611 to this issue.


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

	Issue introduced in 6.0 with commit ce61327ce989b63c0bd1cc7afee00e218ee696ac and fixed in 6.18.45 with commit 68787940274ec89f41dc91b1a68ee1a16a90735f
	Issue introduced in 6.0 with commit ce61327ce989b63c0bd1cc7afee00e218ee696ac and fixed in 7.1.9 with commit 3c837266a734e2a22b24d2d567404a501d405835
	Issue introduced in 6.0 with commit ce61327ce989b63c0bd1cc7afee00e218ee696ac and fixed in 7.2 with commit 1c8629651cb54f7b51db8fc0b1a9944e4a4b0f5e

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-2026-74611
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/tls/tls_sw.c
	tools/testing/selftests/net/tls.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/68787940274ec89f41dc91b1a68ee1a16a90735f
	https://git.kernel.org/stable/c/3c837266a734e2a22b24d2d567404a501d405835
	https://git.kernel.org/stable/c/1c8629651cb54f7b51db8fc0b1a9944e4a4b0f5e