CVE-2025-38488

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

smb: client: fix use-after-free in crypt_message when using async crypto

The CVE-2024-50047 fix removed asynchronous crypto handling from crypt_message(), assuming all crypto operations are synchronous. However, when hardware crypto accelerators are used, this can cause use-after-free crashes:

crypt_message() // Allocate the creq buffer containing the req creq = smb2_get_aead_req(…, &req);

// Async encryption returns -EINPROGRESS immediately
rc = enc ? crypto_aead_encrypt(req) : crypto_aead_decrypt(req);

// Free creq while async operation is still in progress
kvfree_sensitive(creq, ...);

Hardware crypto modules often implement async AEAD operations for performance. When crypto_aead_encrypt/decrypt() returns -EINPROGRESS, the operation completes asynchronously. Without crypto_wait_req(), the function immediately frees the request buffer, leading to crashes when the driver later accesses the freed memory.

This results in a use-after-free condition when the hardware crypto driver later accesses the freed request structure, leading to kernel crashes with NULL pointer dereferences.

The issue occurs because crypto_alloc_aead() with mask=0 doesnt guarantee synchronous operation. Even without CRYPTO_ALG_ASYNC in the mask, async implementations can be selected.

Fix by restoring the async crypto handling:

• DECLARE_CRYPTO_WAIT(wait) for completion tracking
• aead_request_set_callback() for async completion notification
• crypto_wait_req() to wait for operation completion

This ensures the request buffer isnt freed until the crypto operation completes, whether synchronous or asynchronous, while preserving the CVE-2024-50047 fix.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/15a0a5de49507062bc3be4014a403d8cea5533de
• https://git.kernel.org/stable/c/2a76bc2b24ed889a689fb1c9015307bf16aafb5b
• https://git.kernel.org/stable/c/5d047b12f86cc3b9fde1171c02d9bccf4dba0632
• https://git.kernel.org/stable/c/6550b2bef095d0dd2d2c8390d2ea4c3837028833
• https://git.kernel.org/stable/c/8ac90f6824fc44d2e55a82503ddfc95defb19ae0
• https://git.kernel.org/stable/c/9a1d3e8d40f151c2d5a5f40c410e6e433f62f438
• https://git.kernel.org/stable/c/b220bed63330c0e1733dc06ea8e75d5b9962b6b6
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html