CVE-2024-36928 (Moderate severity, published 2024-05-29)
CVSS score: 4.1 (CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H)
CWE: CWE-476
Description: In the Linux kernel, the following vulnerability has been resolved:

s390/qeth: Fix kernel panic after setting hsuid

Symptom:
When the hsuid attribute is set for the first time on an IQD Layer3
device while the corresponding network interface is already UP,
the kernel will try to execute a napi function pointer that is NULL.

Example:
---------------------------------------------------------------------------
[ 2057.572696] illegal operation: 0001 ilc:1 [#1] SMP
[ 2057.572702] Modules linked in: af_iucv qeth_l3 zfcp scsi_transport_fc sunrpc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6
nft_reject nft_ct nf_tables_set nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables libcrc32c nfnetlink ghash_s390 prng xts aes_s390 des_s390 de
s_generic sha3_512_s390 sha3_256_s390 sha512_s390 vfio_ccw vfio_mdev mdev vfio_iommu_type1 eadm_sch vfio ext4 mbcache jbd2 qeth_l2 bridge stp llc dasd_eckd_mod qeth dasd_mod
 qdio ccwgroup pkey zcrypt
[ 2057.572739] CPU: 6 PID: 60182 Comm: stress_client Kdump: loaded Not tainted 4.18.0-541.el8.s390x #1
[ 2057.572742] Hardware name: IBM 3931 A01 704 (LPAR)
[ 2057.572744] Krnl PSW : 0704f00180000000 0000000000000002 (0x2)
[ 2057.572748]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:3 PM:0 RI:0 EA:3
[ 2057.572751] Krnl GPRS: 0000000000000004 0000000000000000 00000000a3b008d8 0000000000000000
[ 2057.572754]            00000000a3b008d8 cb923a29c779abc5 0000000000000000 00000000814cfd80
[ 2057.572756]            000000000000012c 0000000000000000 00000000a3b008d8 00000000a3b008d8
[ 2057.572758]            00000000bab6d500 00000000814cfd80 0000000091317e46 00000000814cfc68
[ 2057.572762] Krnl Code:#0000000000000000: 0000                illegal
                         >0000000000000002: 0000                illegal
                          0000000000000004: 0000                illegal
                          0000000000000006: 0000                illegal
                          0000000000000008: 0000                illegal
                          000000000000000a: 0000                illegal
                          000000000000000c: 0000                illegal
                          000000000000000e: 0000                illegal
[ 2057.572800] Call Trace:
[ 2057.572801] ([<00000000ec639700>] 0xec639700)
[ 2057.572803]  [<00000000913183e2>] net_rx_action+0x2ba/0x398
[ 2057.572809]  [<0000000091515f76>] __do_softirq+0x11e/0x3a0
[ 2057.572813]  [<0000000090ce160c>] do_softirq_own_stack+0x3c/0x58
[ 2057.572817] ([<0000000090d2cbd6>] do_softirq.part.1+0x56/0x60)
[ 2057.572822]  [<0000000090d2cc60>] __local_bh_enable_ip+0x80/0x98
[ 2057.572825]  [<0000000091314706>] __dev_queue_xmit+0x2be/0xd70
[ 2057.572827]  [<000003ff803dd6d6>] afiucv_hs_send+0x24e/0x300 [af_iucv]
[ 2057.572830]  [<000003ff803dd88a>] iucv_send_ctrl+0x102/0x138 [af_iucv]
[ 2057.572833]  [<000003ff803de72a>] iucv_sock_connect+0x37a/0x468 [af_iucv]
[ 2057.572835]  [<00000000912e7e90>] __sys_connect+0xa0/0xd8
[ 2057.572839]  [<00000000912e9580>] sys_socketcall+0x228/0x348
[ 2057.572841]  [<0000000091514e1a>] system_call+0x2a6/0x2c8
[ 2057.572843] Last Breaking-Event-Address:
[ 2057.572844]  [<0000000091317e44>] __napi_poll+0x4c/0x1d8
[ 2057.572846]
[ 2057.572847] Kernel panic - not syncing: Fatal exception in interrupt
-------------------------------------------------------------------------------------------

Analysis:
There is one napi structure per out_q: card->qdio.out_qs[i].napi
The napi.poll functions are set during qeth_open().

Since
commit 1cfef80d4c2b ("s390/qeth: Don't call dev_close/dev_open (DOWN/UP)")
qeth_set_offline()/qeth_set_online() no longer call dev_close()/
dev_open(). So if qeth_free_qdio_queues() cleared
card->qdio.out_qs[i].napi.poll while the network interface was UP and the
card was offline, they are not set again.

Reproduction:
chzdev -e $devno layer2=0
ip link set dev $network_interface up
echo 0 > /sys/bus/ccw
---truncated---
Statement: Within regulated environments, a combination of the following controls acts as a significant barrier to successfully exploiting a CWE-476: NULL Pointer Dereference vulnerability and therefore downgrades the severity of this particular CVE from Moderate to Low.

The platform incorporates secure engineering principles and controls to enforce secure coding practices, including proper memory handling and error checking, reducing the likelihood of null pointer dereference vulnerabilities. Coding standards, tools, and processes support early detection and prevention of memory-related flaws. Static code analysis identifies null dereference and related issues during development, while system monitoring detects memory errors and anomalous behavior in the event of exploitation. Additionally, the platform leverages memory protection mechanisms such as Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) to strengthen resilience against memory-related vulnerabilities.