CVE-2026-74550: net: do not send ICMP/NDISC Redirects when peer allocation fails

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

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

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

net: do not send ICMP/NDISC Redirects when peer allocation fails

When inet_getpeer_v4() or inet_getpeer_v6() fails to allocate a peer entry
under memory pressure or tree size caps, redirect handlers previously fell
back to sending un-rate-limited ICMP/NDISC Redirect messages.

In IPv4, ip_rt_send_redirect() called icmp_send() directly when peer == NULL.
In IPv6, ip6_forward() and ndisc_send_redirect() passed a NULL peer into
inet_peer_xrlim_allow(), which returned true when peer == NULL.

Because ICMP/NDISC Redirects are not part of the default global rate limit
mask (sysctl_icmp_ratemask), sending redirects when peer == NULL creates
an un-rate-limited ICMP packet storm.

Fix this by failing closed in ip_rt_send_redirect(), ip6_forward(), and
ndisc_send_redirect() when peer is NULL.

The Linux kernel CVE team has assigned CVE-2026-74550 to this issue.


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

	Issue introduced in 2.6.39 with commit 92d8682926342d2b6aa5b2ecc02221e00e1573a0 and fixed in 6.6.151 with commit f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1
	Issue introduced in 2.6.39 with commit 92d8682926342d2b6aa5b2ecc02221e00e1573a0 and fixed in 6.12.103 with commit 21666f7af49a90ef44d474916b8ef4402dfd74f5
	Issue introduced in 2.6.39 with commit 92d8682926342d2b6aa5b2ecc02221e00e1573a0 and fixed in 6.18.44 with commit 5ec5f00fc606a6df8434948c4552b3cb1176595d
	Issue introduced in 2.6.39 with commit 92d8682926342d2b6aa5b2ecc02221e00e1573a0 and fixed in 7.1.8 with commit 828f6670d110ff2bf44c743037b38badc315704c
	Issue introduced in 2.6.39 with commit 92d8682926342d2b6aa5b2ecc02221e00e1573a0 and fixed in 7.2-rc6 with commit dbc3791e3b2472e1ccc08947e0f83b443470ff4f

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-2026-74550
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/ipv4/route.c
	net/ipv6/ip6_output.c
	net/ipv6/ndisc.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/f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1
	https://git.kernel.org/stable/c/21666f7af49a90ef44d474916b8ef4402dfd74f5
	https://git.kernel.org/stable/c/5ec5f00fc606a6df8434948c4552b3cb1176595d
	https://git.kernel.org/stable/c/828f6670d110ff2bf44c743037b38badc315704c
	https://git.kernel.org/stable/c/dbc3791e3b2472e1ccc08947e0f83b443470ff4f