Bug 2536806 (CVE-2026-90170)

Summary: CVE-2026-90170 kernel: ksmbd: validate ipc response length before dereferencing its fields
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in ksmbd, a component of the Linux kernel. This vulnerability occurs because the `ipc_validate_msg()` function reads length fields from an Inter-Process Communication (IPC) response buffer before verifying if the buffer is large enough. A local attacker, by providing a specially crafted short IPC response, can trigger an out-of-bounds read. This can lead to a system crash, resulting in a denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-17 19:35:11 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: validate ipc response length before dereferencing its fields

ipc_validate_msg() computes the expected message size by reading length
fields out of the response buffer supplied by the userspace ksmbd daemon
(payload_sz, session_key_len, ngroups, ...).  Those fields are read before
the buffer is verified to be large enough to contain the struct they belong
to, so a short response makes the read land past the end of the allocation.

handle_response() sizes entry->response purely from the netlink attribute
length (nla_len()) and only guards the leading handle read, so the daemon
can install a response as small as the kmalloc-8 object seen below.  When
ipc_msg_send_request() then calls ipc_validate_msg() for a
KSMBD_EVENT_RPC_REQUEST, the cast to struct ksmbd_rpc_command reads
resp->payload_sz at offset 8 of an 8-byte allocation:

[ 3697.841381] ==================================================================
[ 3697.844099] BUG: KASAN: slab-out-of-bounds in ipc_msg_send_request+0x763/0x800
[ 3697.846604] Read of size 4 at addr ffff888105f95910 by task kworker/4:3/20682
[ 3697.849061]
[ 3697.849801] CPU: 4 UID: 0 PID: 20682 Comm: kworker/4:3 Not tainted 7.2.0-rc3-next-20260717-virtme #117 PREEMPT(lazy)
[ 3697.850077] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 3697.850303] Workqueue: ksmbd-io handle_ksmbd_work
[ 3697.850592] Call Trace:
[ 3697.850794]  <TASK>
[ 3697.850952]  __dump_stack+0x21/0x60
[ 3697.851239]  dump_stack_lvl+0xc2/0x100
[ 3697.851528]  print_address_description+0x77/0x200
[ 3697.851816]  ? ipc_msg_send_request+0x763/0x800
[ 3697.852024]  print_report+0x58/0x70
[ 3697.852316]  kasan_report+0x117/0x150
[ 3697.852585]  ? down_write+0x146/0x1f0
[ 3697.852809]  ? ipc_msg_send_request+0x763/0x800
[ 3697.853082]  ipc_msg_send_request+0x763/0x800
[ 3697.853385]  ? __pfx_ipc_msg_send_request+0x10/0x10
[ 3697.853604]  ? kasan_unpoison+0x48/0x70
[ 3697.853936]  ? __pfx___up_read+0x10/0x10
[ 3697.854221]  ksmbd_rpc_ioctl+0x380/0x520
[ 3697.854542]  ? __pfx_ksmbd_rpc_ioctl+0x10/0x10
[ 3697.854757]  ? kasan_unpoison+0x48/0x70
[ 3697.854962]  ? copy_from_kernel_nofault+0x32c/0x4e0
[ 3697.855166]  ? kasan_unpoison+0x48/0x70
[ 3697.855416]  fsctl_pipe_transceive+0x139/0x7a0
[ 3697.855705]  ? __pfx_copy_from_kernel_nofault+0x10/0x10
[ 3697.855937]  ? __pfx_fsctl_pipe_transceive+0x10/0x10
[ 3697.856388]  ? __sanitizer_cov_trace_switch+0x7b/0x140
[ 3697.856620]  smb2_ioctl+0x1141/0x3420
[ 3697.856994]  ? __pfx_smb2_ioctl+0x10/0x10
[ 3697.857182]  ? get_smb2_cmd_val+0xe3/0x1c0
[ 3697.857655]  handle_ksmbd_work+0x9ad/0x15e0
[ 3697.858034]  ? __pfx_handle_ksmbd_work+0x10/0x10
[ 3697.858251]  ? lock_release+0xf7/0x360
[ 3697.858466]  ? process_scheduled_works+0x954/0x1600
[ 3697.858698]  ? process_scheduled_works+0x954/0x1600
[ 3697.858905]  process_scheduled_works+0xc22/0x1600
[ 3697.859368]  ? __pfx_process_scheduled_works+0x10/0x10
[ 3697.859637]  ? __pfx_assign_work+0x10/0x10
[ 3697.859896]  ? lock_is_held_type+0x7b/0x110
[ 3697.860146]  worker_thread+0x975/0xee0
[ 3697.860524]  ? __pfx_do_raw_spin_lock+0x10/0x10
[ 3697.860830]  ? __kthread_parkme+0x21e/0x260
[ 3697.861105]  kthread+0x3a6/0x490
[ 3697.861423]  ? __pfx_worker_thread+0x10/0x10
[ 3697.861643]  ? __pfx_kthread+0x10/0x10
[ 3697.861878]  ret_from_fork+0x55a/0xa20
[ 3697.862194]  ? __pfx_ret_from_fork+0x10/0x10
[ 3697.862480]  ? __pfx_kthread+0x10/0x10
[ 3697.862714]  ret_from_fork_asm+0x1a/0x30
[ 3697.862965]  </TASK>
[ 3697.863039]
[ 3697.938882] Allocated by task 20761:
[ 3697.940257]  kasan_save_track+0x3e/0x80
[ 3697.941782]  __kasan_kmalloc+0x72/0x90
[ 3697.943228]  __kvmalloc_node_noprof+0x3e9/0x6a0
[ 3697.944948]  handle_generic_event+0x59b/0x750
[ 3697.946592]  genl_family_rcv_msg_doit+0x3d6/0x560
[ 3697.946977]  genl_rcv_msg+0x67c/0x900
[ 3697.947224]  netlink_rcv_skb+0x286/0x580
[ 3697.947488]  genl_rcv+0x2d/0x80
[ 3
---truncated---
Comment 1 Keith Grant 2026-09-23 19:38:27 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-90170.mbox