CVE-2024-43817 in Linux
요약
\~에 의해 VulDB • 2026. 06. 30.
Based on the crash trace and register information provided, here is a detailed analysis of the kernel panic.
### 1. Crash Summary * **Type:** Kernel Oops / Panic due to invalid memory access or assertion failure in network stack fragmentation logic. * **Triggering System Call:** `sendto` (via packet socket). * **Faulty Component:** IPv4 Fragmentation (`ip_do_fragment`) within an IPIP/SIT tunnel context. * **Tool:** Syzkaller (fuzzing tool), indicating this is likely a reproducible bug in edge cases of network packet handling.
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### 2. Key Register Analysis
#### `CR2: 0x000000002000f000` * **Meaning:** This register holds the faulting virtual address if it was a page fault (e.g., NULL pointer dereference, out-of-bounds access). * **Analysis:** The value `0x2000f000` is **not** zero. It suggests an invalid or unmapped memory region that is not simply a NULL/NULL+page dereference. This could indicate: * A use-after-free where the freed page was reallocated and then accessed incorrectly. * An out-of-bounds access into a slab object. * Corrupted pointer arithmetic leading to an invalid address.
#### `DR6: 0x00000000fffe0ff0` & `DR7: 0x0000000000000400` * **Meaning:** Debug registers. The presence of non-zero debug registers suggests that hardware breakpoints or single-step debugging might have been active, but more commonly in crash dumps from fuzzers like Syzkaller, this indicates the CPU was interrupted during execution with debug state preserved. It doesn't directly explain the bug but confirms the context.
#### `CS: 0x10 DS/ES: 0x00` * Standard kernel mode segment selectors (DS/ES being zero is normal in long mode when using flat memory model).
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### 3. Call Trace Analysis
The call trace reveals a clear path from user-space to the crash point:
```text packet_sendmsg -> ipip6_tunnel_xmit -> ip_do_fragment +0xa1b/0x18b0 ```
#### Step-by-Step Breakdown: 1. **`__sys_sendto` / `sock_sendmsg_nosec`**: User-space application calls `send()` or `sendto()`. 2. **`packet_snd` / `packet_xmit`**: The socket is a **PACKET_SOCKET** (AF_PACKET). This means the user program is injecting raw Ethernet frames directly into the network stack. 3. **`dev_hard_start_xmit` → `__netdev_start_xmit`**: The packet enters the device driver layer. 4. **`sit_tunnel_xmit` / `ipip6_tunnel_xmit` (`net/ipv6/sit.c:1076`)**: * The injected frame is being processed by an **SIT (IPv6-in-IPv4) tunnel** or IPIP tunnel interface. * SIT tunnels encapsulate IPv6 packets inside IPv4 headers. However, since the input came from a raw packet socket (`AF_PACKET`), it's possible that malformed or unexpected frames are triggering unusual code paths in the tunneling logic. 5. **`ip_local_out` → `dst_output`**: The tunneled packet is prepared for local output (or forwarding). 6. **`NF_HOOK_COND` / `ip_finish_output`**: Netfilter hooks and IP output processing occur. 7. **`__ip_finish_output_gso` → `ip_fragment.constprop.0` → `ip_do_fragment+0xa1b/0x18b0` (`net/ipv4/ip_output.c:777`)**: * The packet exceeds the MTU of the outgoing interface, triggering **IPv4 fragmentation**. * The crash occurs inside `ip_do_fragment`, specifically at offset `+0xa1b`.
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### 4. Root Cause Hypothesis
The bug is in **`net/ipv4/ip_output.c:777`** within the function `ip_do_fragment()`. Given that Syzkaller found this, it's likely a race condition, missing bounds check, or incorrect pointer arithmetic when handling fragmented packets from tunnel interfaces.
#### Likely Scenarios: 1. **Invalid Sk_buff Chain Handling:** * In `ip_do_fragment`, the kernel splits an original sk_buff into multiple fragments. If the
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