CVE-2026-31533

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

net/tls: fix use-after-free in -EBUSY error path of tls_do_encryption

The -EBUSY handling in tls_do_encryption(), introduced by commit 859054147318 (net: tls: handle backlogging of crypto requests), has a use-after-free due to double cleanup of encrypt_pending and the scatterlist entry.

When crypto_aead_encrypt() returns -EBUSY, the request is enqueued to the cryptd backlog and the async callback tls_encrypt_done() will be invoked upon completion. That callback unconditionally restores the scatterlist entry (sge->offset, sge->length) and decrements ctx->encrypt_pending. However, if tls_encrypt_async_wait() returns an error, the synchronous error path in tls_do_encryption() performs the same cleanup again, double-decrementing encrypt_pending and double-restoring the scatterlist.

The double-decrement corrupts the encrypt_pending sentinel (initialized to 1), making tls_encrypt_async_wait() permanently skip the wait for pending async callbacks. A subsequent sendmsg can then free the tls_rec via bpf_exec_tx_verdict() while a cryptd callback is still pending, resulting in a use-after-free when the callback fires on the freed record.

Fix this by skipping the synchronous cleanup when the -EBUSY async wait returns an error, since the callback has already handled encrypt_pending and sge restoration.

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 Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.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/02f3ecadb23558bbe068e6504118f1b712d4ece0
• https://git.kernel.org/stable/c/0e43e0a3c94044acc74b8e0927c27972eb5a59e8
• https://git.kernel.org/stable/c/2694d408b0e595024e0fc1d64ff9db0358580f74
• https://git.kernel.org/stable/c/414fc5e5a5aff776c150f1b86770e0a25a35df3a
• https://git.kernel.org/stable/c/5d70eb25b41e9b010828cd12818b06a0c3b04412
• https://git.kernel.org/stable/c/a9b8b18364fffce4c451e6f6fd218fa4ab646705
• https://git.kernel.org/stable/c/aa9facde6c5005205874c37db3fd25799d741baf