CVE-2024-26614 in Linux
Sumário
de VulDB • 27/05/2026
Based on the stack trace and the race condition analysis provided, here is a detailed breakdown of the issue.
### **Summary of the Issue** This is a **use-after-free (UAF)** or **race condition** bug in the Linux TCP stack, specifically involving the interaction between **TCP connection establishment** (`tcp_v4_rcv` processing a SYN-ACK) and **socket disconnection** (`inet_shutdown` -> `tcp_disconnect`).
The core problem is that **Thread B** disconnects and frees the socket (`sk`) while **Thread A** is still processing a received TCP packet for that same socket, leading to a potential crash or memory corruption.
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### **Detailed Analysis**
#### **1. Stack Trace Breakdown** The stack trace shows the execution path of **Thread A**: 1. **`entry_SYSCALL_64`**: The process started a system call. 2. **`__x64_sys_connect`**: The application called `connect()`. 3. **`inet_stream_connect`**: The kernel's TCP connect implementation. 4. **`__inet_stream_connect`**: Internal connect logic. 5. **`inet_wait_for_connect`**: The thread is waiting for the connection to complete (blocking in `connect()`). 6. **`release_sock` / `__release_sock`**: The socket lock is being released or managed. 7. **`tcp_v4_do_rcv`**: The kernel is processing a received TCP packet (likely the SYN-ACK from the server). 8. **`tcp_rcv_state_process`**: State machine processing for TCP. 9. **`tcp_rcv_synsent_state_process`**: Handling the SYN-ACK in the `SYN_SENT` state. 10. **`__tcp_transmit_skb`**: The kernel is preparing to send a packet (likely the final ACK to complete the 3-way handshake). 11. **`__ip_queue_xmit` / `ip_finish_output2` / `__dev_queue_xmit`**: The packet is being queued for transmission.
**Key Insight**: The crash occurs during the transmission of the final ACK after receiving a SYN-ACK. However, the race condition analysis suggests the socket was freed by another thread.
#### **2. Race Condition Analysis (Thread A vs. Thread B)**
| Thread A (Receiver/Transmitter) | Thread B (Disconnector) | | :--- | :--- | | `tcp_v4_rcv` receives a TCP packet (SYN-ACK). | Calls `inet_shutdown()` on the same socket. | | Calls `tcp_check_req()` to validate the request. | Calls `tcp_disconnect()`. | | ... | Sets socket state to `TCP_CLOSE`. | | Calls `inet_csk_complete_hashdance()` to finalize the connection. | ... | | Calls `inet_csk_reqsk_queue_add()` to add the request to the accept queue. | **Socket memory is freed/released.** | | **CRASH**: Tries to access freed memory. | |
#### **3. Root Cause** The bug lies in the **lack of proper synchronization** between the socket's state and the packet processing path.
1. **Thread B** calls `inet_shutdown()`, which leads to `tcp_disconnect()`. 2. `tcp_disconnect()` sets the socket state to `TCP_CLOSE` and may initiate the freeing of the socket structure (`sk`). 3. **However**, **Thread A** is already in the middle of processing a packet for this socket (`tcp_v4_rcv`). 4. The kernel's packet receive path (`tcp_v4_rcv`) does not immediately check if the socket has been disconnected/freed. It proceeds to `tcp_check_req` and `inet_csk_complete_hashdance`. 5. If `tcp_disconnect()` frees the `sk` structure while `tcp_v4_rcv` is still holding a reference or accessing it, a **Use-After-Free** occurs.
#### **4. Why This Happens** - **Asynchronous Nature**: Network packets can arrive at any time, even after a user-space thread has initiated a disconnect. - **Locking Issues**: The socket lock (`sk_lock`) might not be held consistently across the disconnect and packet receive paths, or the disconnect path does not properly synchronize with the receive path. - **Reference Counting**: The socket's reference count might drop to zero and be freed before the receive path finishes processing the packet.
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### **Potential Fixes**
1. **Synchronize Disconnect and Receive**: - Ensure that `tcp_disconnect()` waits for all pending packet processing to complete before freeing the socket. - Use proper locking (e.g., `sk_lock`) to prevent `tcp
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