CVE-2026-64048: net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot

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

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

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

net/smc: reject CHID-0 ACCEPT that matches an empty ism_dev slot

On the SMC-D client, slot 0 of ini->ism_dev[]/ini->ism_chid[] is
reserved for an SMC-Dv1 device. smc_find_ism_v2_device_clnt()
populates V2 entries starting at index 1, so when no V1 device is
selected slot 0 is left in its kzalloc()'ed state with ism_dev[0] ==
NULL and ism_chid[0] == 0.

smc_v2_determine_accepted_chid() then matches the peer's CHID against
the array starting from index 0 using the CHID alone. A malicious
peer replying to a SMC-Dv2-only proposal with d1.chid == 0 matches
the empty slot, ini->ism_selected becomes 0, and the subsequent
ism_dev[0]->lgr_lock dereference in smc_conn_create() faults at
offsetof(struct smcd_dev, lgr_lock) == 0x68:

  BUG: KASAN: null-ptr-deref in _raw_spin_lock_bh+0x79/0xe0
  Write of size 4 at addr 0000000000000068 by task exploit/144
  Call Trace:
   _raw_spin_lock_bh
   smc_conn_create (net/smc/smc_core.c:1997)
   __smc_connect (net/smc/af_smc.c:1447)
   smc_connect (net/smc/af_smc.c:1720)
   __sys_connect
   __x64_sys_connect
   do_syscall_64

Require ism_dev[i] to be non-NULL before accepting a CHID match.

The Linux kernel CVE team has assigned CVE-2026-64048 to this issue.


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

	Issue introduced in 5.10 with commit a7c9c5f4af7f6098da68705fc5d86565d0728ef7 and fixed in 6.1.175 with commit 6927cacf2b10d4fa80c1a2d407512ef9397c59c6
	Issue introduced in 5.10 with commit a7c9c5f4af7f6098da68705fc5d86565d0728ef7 and fixed in 6.6.142 with commit d38ba387244e5c5f7db3e11ea98bc2c7beccb0c0
	Issue introduced in 5.10 with commit a7c9c5f4af7f6098da68705fc5d86565d0728ef7 and fixed in 6.12.92 with commit 53eb7bd09aace72fa17510d80e0caf5ca058c231
	Issue introduced in 5.10 with commit a7c9c5f4af7f6098da68705fc5d86565d0728ef7 and fixed in 6.18.34 with commit afa9036b8c9963947b487c36e332df6a42c96fcb
	Issue introduced in 5.10 with commit a7c9c5f4af7f6098da68705fc5d86565d0728ef7 and fixed in 7.0.11 with commit 65edb3b0822cfe5041be8fbabebd57e2e5ad9f4e
	Issue introduced in 5.10 with commit a7c9c5f4af7f6098da68705fc5d86565d0728ef7 and fixed in 7.1 with commit 277740023def559a4a2ddc3e8e784ee37a0f16a9

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-2026-64048
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/smc/af_smc.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/6927cacf2b10d4fa80c1a2d407512ef9397c59c6
	https://git.kernel.org/stable/c/d38ba387244e5c5f7db3e11ea98bc2c7beccb0c0
	https://git.kernel.org/stable/c/53eb7bd09aace72fa17510d80e0caf5ca058c231
	https://git.kernel.org/stable/c/afa9036b8c9963947b487c36e332df6a42c96fcb
	https://git.kernel.org/stable/c/65edb3b0822cfe5041be8fbabebd57e2e5ad9f4e
	https://git.kernel.org/stable/c/277740023def559a4a2ddc3e8e784ee37a0f16a9