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Linux kernel source tree
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
[ 3697.947706] netlink_unicast+0x937/0xb70
[ 3697.947993] netlink_sendmsg+0x977/0xc10
[ 3697.948268] __sock_sendmsg+0x264/0x2d0
[ 3697.948536] __sys_sendto+0x4de/0x690
[ 3697.948789] __x64_sys_sendto+0x173/0x380
[ 3697.949069] do_syscall_64+0x13d/0x420
[ 3697.949328] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 3697.949662]
[ 3697.949779] The buggy address belongs to the object at ffff888105f95908
[ 3697.949779] which belongs to the cache kmalloc-8 of size 8
[ 3697.950550] The buggy address is located 0 bytes to the right of
[ 3697.950550] allocated 8-byte region [ffff888105f95908, ffff888105f95910)
[ 3697.951455]
[ 3697.951574] The buggy address belongs to the physical page:
[ 3697.951958] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888105f951b8 pfn:0x105f95
[ 3697.952571] flags: 0x100000000000200(workingset|node=0|zone=2)
[ 3697.952973] page_type: f5(slab)
[ 3697.953198] raw: 0100000000000200 ffff888100042640 ffffea0004063610 ffff888100040588
[ 3697.953707] raw: ffff888105f951b8 00000000001c000e 00000000f5000000 0000000000000000
[ 3697.954240] page dumped because: kasan: bad access detected
[ 3697.954616]
[ 3697.954734] Memory state around the buggy address:
[ 3697.955063] ffff888105f95800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fa
[ 3697.955534] ffff888105f95880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 3697.956006] >ffff888105f95900: fc 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 3697.956477] ^
[ 3697.956728] ffff888105f95980: fc fc fc fa fc fc fc fc fc fc fc fc fc fc fc fc
[ 3697.957202] ffff888105f95a00: fc fc fc fc fc fa fc fc fc fc fc fc fc fc fc fc
[ 3697.957671] ==================================================================
The final "entry->msg_sz != msg_sz" comparison cannot help: the offending
read has already happened by the time it runs. Every case in the switch
shares this pattern.
Floor entry->msg_sz against the base struct of each event type before
dereferencing any of its length fields. On failure ipc_msg_send_request()
already frees the response and returns NULL, so callers stay safe.
The malformed message originates from the ksmbd.mountd daemon over genl
netlink rather than a remote SMB client, so triggering it requires a buggy
or compromised daemon; it is still an out-of-bounds read the validator is
meant to prevent.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst