CVE-2025-40052 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix crypto buffers in non-linear memory
The crypto API, through the scatterlist API, expects input buffers to be in linear memory. We handle this with the cifs_sg_set_buf() helper that converts vmalloc'd memory to their corresponding pages.
However, when we allocate our aead_request buffer (@creq in smb2ops.c::crypt_message()), we do so with kvzalloc(), which possibly puts aead_request->__ctx in vmalloc area.
AEAD algorithm then uses ->__ctx for its private/internal data and operations, and uses sg_set_buf() for such data on a few places.
This works fine as long as @creq falls into kmalloc zone (small requests) or vmalloc'd memory is still within linear range.
Tasks' stacks are vmalloc'd by default (CONFIG_VMAP_STACK=y), so too many tasks will increment the base stacks' addresses to a point where virt_addr_valid(buf) will fail (BUG() in sg_set_buf()) when that happens.
In practice: too many parallel reads and writes on an encrypted mount will trigger this bug.
To fix this, always alloc @creq with kmalloc() instead. Also drop the @sensitive_size variable/arguments since kfree_sensitive() doesn't need it.
Backtrace:
[ 945.272081] ------------[ cut here ]------------
[ 945.272774] kernel BUG at include/linux/scatterlist.h:209!
[ 945.273520] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC NOPTI
[ 945.274412] CPU: 7 UID: 0 PID: 56 Comm: kworker/u33:0 Kdump: loaded Not tainted 6.15.0-lku-11779-g8e9d6efccdd7-dirty #1 PREEMPT(voluntary)
[ 945.275736] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-2-gc13ff2cd-prebuilt.qemu.org 04/01/2014
[ 945.276877] Workqueue: writeback wb_workfn (flush-cifs-2)
[ 945.277457] RIP: 0010:crypto_gcm_init_common+0x1f9/0x220
[ 945.278018] Code: b0 00 00 00 48 83 c4 08 5b 5d 41 5c 41 5d 41 5e 41 5f c3 cc cc cc cc 48 c7 c0 00 00 00 80 48 2b 05 5c 58 e5 00 e9 58 ff ff ff <0f> 0b 0f 0b 0f 0b 0f 0b 0f 0b 0f 0b 48 c7 04 24 01 00 00 00 48 8b
[ 945.279992] RSP: 0018:ffffc90000a27360 EFLAGS: 00010246
[ 945.280578] RAX: 0000000000000000 RBX: ffffc90001d85060 RCX: 0000000000000030
[ 945.281376] RDX: 0000000000080000 RSI: 0000000000000000 RDI: ffffc90081d85070
[ 945.282145] RBP: ffffc90001d85010 R08: ffffc90001d85000 R09: 0000000000000000
[ 945.282898] R10: ffffc90001d85090 R11: 0000000000001000 R12: ffffc90001d85070
[ 945.283656] R13: ffff888113522948 R14: ffffc90001d85060 R15: ffffc90001d85010
[ 945.284407] FS: 0000000000000000(0000) GS:ffff8882e66cf000(0000) knlGS:0000000000000000
[ 945.285262] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 945.285884] CR2: 00007fa7ffdd31f4 CR3: 000000010540d000 CR4: 0000000000350ef0
[ 945.286683] Call Trace:
[ 945.286952] <TASK>
[ 945.287184] ? crypt_message+0x33f/0xad0 [cifs]
[ 945.287719] crypto_gcm_encrypt+0x36/0xe0
[ 945.288152] crypt_message+0x54a/0xad0 [cifs]
[ 945.288724] smb3_init_transform_rq+0x277/0x300 [cifs]
[ 945.289300] smb_send_rqst+0xa3/0x160 [cifs]
[ 945.289944] cifs_call_async+0x178/0x340 [cifs]
[ 945.290514] ? __pfx_smb2_writev_callback+0x10/0x10 [cifs]
[ 945.291177] smb2_async_writev+0x3e3/0x670 [cifs]
[ 945.291759] ? find_held_lock+0x32/0x90
[ 945.292212] ? netfs_advance_write+0xf2/0x310
[ 945.292723] netfs_advance_write+0xf2/0x310
[ 945.293210] netfs_write_folio+0x346/0xcc0
[ 945.293689] ? __pfx__raw_spin_unlock_irq+0x10/0x10
[ 945.294250] netfs_writepages+0x117/0x460
[ 945.294724] do_writepages+0xbe/0x170
[ 945.295152] ? find_held_lock+0x32/0x90
[ 945.295600] ? kvm_sched_clock_read+0x11/0x20
[ 945.296103] __writeback_single_inode+0x56/0x4b0
[ 945.296643] writeback_sb_inodes+0x229/0x550
[ 945.297140] __writeback_inodes_wb+0x4c/0xe0
[ 945.297642] wb_writeback+0x2f1/0x3f0
[ 945.298069] wb_workfn+0x300/0x490
[ 945.298472] process_one_work+0x1fe/0x590
[ 945.298949] worker_thread+0x1ce/0x3c0
[ 945.299397] ? __pfx_worker_thread+0x10/0x10
[ 945.299900] kthr
---truncated---
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability described in CVE-2025-40052 resides within the Linux kernel's Server Message Block (SMB) client implementation, specifically affecting encrypted SMB mounts. This issue stems from a fundamental incompatibility between how the kernel's cryptographic API handles memory buffers and how the SMB client allocates memory for cryptographic operations. The core problem manifests when the kernel's Advanced Encryption Algorithm (AEAD) subsystem attempts to process data that has been allocated in non-linear memory regions, which violates the expectations of the scatterlist API used by the crypto framework. The vulnerability is particularly relevant in environments where high concurrency and parallel I/O operations occur, such as enterprise file servers with extensive SMB client usage.
The technical flaw occurs in the `crypt_message()` function within the SMB2 operations module where an `aead_request` buffer is allocated using `kvzalloc()`. This allocation method can place the buffer in vmalloc'd memory, which is not guaranteed to be linearly mapped in kernel virtual address space. The cryptographic algorithms then utilize the `__ctx` field of the `aead_request` structure for internal operations, including calls to `sg_set_buf()`, which expects linear memory addresses. When the buffer address falls outside the valid linear memory range, the `virt_addr_valid()` check in `sg_set_buf()` triggers a kernel BUG, resulting in a system panic. This is especially problematic because kernel stacks are allocated via vmalloc by default when `CONFIG_VMAP_STACK=y` is enabled, and excessive parallel operations can push stack addresses beyond the linear memory boundaries, causing the failure.
The operational impact of this vulnerability is significant for systems running encrypted SMB mounts under high concurrent load. When numerous parallel read and write operations occur simultaneously, the system becomes increasingly likely to trigger the kernel panic, leading to service disruption and potential data loss. This affects enterprise environments where SMB shares are heavily used for file storage and collaboration, particularly in scenarios involving large file transfers or high-throughput applications. The vulnerability essentially creates a denial-of-service condition where the system becomes unstable under normal operational stress, making it particularly dangerous for mission-critical infrastructure.
The fix implemented addresses the root cause by changing the memory allocation strategy for the `aead_request` buffer from `kvzalloc()` to `kmalloc()`, ensuring that the buffer is allocated within the kernel's linear memory space where it can be properly handled by the crypto API. This change prevents the buffer from being placed in vmalloc'd regions that may not be accessible to the scatterlist operations. Additionally, the patch removes the `@sensitive_size` variable and associated arguments since `kfree_sensitive()` does not require this parameter, streamlining the memory management and reducing potential complexity. This remediation aligns with security best practices for memory handling in kernel space, as outlined in CWE-122 (Heap Overflow) and CWE-787 (Out-of-bounds Write), and follows ATT&CK techniques related to system compromise and privilege escalation through kernel vulnerabilities. The fix ensures that cryptographic operations on encrypted SMB mounts can proceed reliably under concurrent workloads without triggering kernel panics, restoring system stability and availability for enterprise file services.