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.

Affected Software

References

• https://git.kernel.org/stable/c/15a0a5de49507062bc3be4014a403d8cea5533de
• https://git.kernel.org/stable/c/2a76bc2b24ed889a689fb1c9015307bf16aafb5b
• https://git.kernel.org/stable/c/8ac90f6824fc44d2e55a82503ddfc95defb19ae0
• https://git.kernel.org/stable/c/9a1d3e8d40f151c2d5a5f40c410e6e433f62f438
• https://git.kernel.org/stable/c/b220bed63330c0e1733dc06ea8e75d5b9962b6b6