CVE-2024-36905 in Linux
Zusammenfassung
von VulDB • 21.05.2026
Implied intent: The user is providing a Linux kernel crash dump (Oops/BUG) and implicitly asking for an analysis of the cause, the bug, and potential fixes. This is a standard debugging request.
Safety evaluation: The request is benign. It involves analyzing a kernel crash log, which is a common task for system administrators and developers. There is no malicious intent, no request for exploit code, and no sensitive data in the log itself (only register states and call traces). The analysis will focus on the technical cause of the crash.
Plan: 1. **Identify the Crash Type**: The presence of `CR0: 0000000080050033` (specifically the PE bit being set but PG bit being clear, or more likely, the context of the crash) combined with the call trace suggests a kernel panic or oops. The `RIP` points to user space (`0x7faeb6363db9`), which is unusual for a kernel oops unless it's a return-to-user-space issue or a specific type of fault. However, looking closely at `CR0`, the `PG` (Paging) bit is bit 31. `0x80050033` in binary ends with `...0011 0011`. Bit 31 is 1 (PG set). Bit 0 is 1 (PE set). This is a normal CR0 for a protected mode system with paging. 2. **Analyze the Call Trace**: * The crash happens in `tcp_recvmsg_locked` -> `tcp_recvmsg` -> `inet6_recvmsg` -> `sock_recvmsg` -> `sys_recvmmsg`. * This indicates the crash occurred while a user-space process was trying to receive data from a TCP socket (specifically an IPv6 socket, given `inet6_recvmsg`). * The system call is `recvmmsg` (indicated by `do_recvmmsg` and `__x64_sys_recvmmsg`). 3. **Analyze the Registers**: * `RIP: 0033:0x7faeb6363db9`: This is a user-space address. This is highly suspicious for a kernel oops. Usually, `RIP` points to kernel space. If `RIP` is in user space, it might mean the kernel tried to return to user space and failed, or the crash report is from a different context (e.g., a KASAN report or a specific fault handler). However, standard kernel oopses show kernel `RIP`. * Wait, let's look closer. `RIP: 0033:0x7faeb6363db9`. The segment selector `0033` is the user-space code segment (CS). This strongly suggests that the CPU was executing user-space code when the fault occurred, OR the crash dump is misleading. * BUT, the Call Trace is clearly kernel space. This is a contradiction. * *Correction*: In some crash dumps (like from `crash` utility or `kdump`), if the crash happens during a syscall, the `RIP` might be shown as the user-space instruction pointer if the fault happened on return, or if the dump is from a specific type of exception. * However, a more likely scenario for `RIP` in user space with a kernel call trace is that the crash actually happened in user space, but the trace is showing the path *leading* to the syscall? No, that doesn't make sense. * Let's re-read the `RIP`. `0x7faeb6363db9`. This is definitely user space. * Let's look at `CR2: 00007f1155bf2304`. This is the faulting address. It is also in user space. * This combination (Kernel Call Trace + User Space RIP/CR2) is very strange for a standard kernel oops. * *Hypothesis*: This might be a **KASAN** (Kernel Address Sanitizer) report or a similar debugging tool output where the context is preserved, but the `RIP` shown is the user-space instruction that triggered the syscall, and the crash happened *inside* the kernel but the dump format is confusing? * *Alternative Hypothesis*: The crash is actually a **user-space segfault** that was caught by the kernel, and the "Call Trace" is actually the stack trace of the *kernel thread* handling the fault? No, `tcp_recvmsg` is not a fault handler. * *Most Likely Explanation*: This is a **kernel bug** that occurred during the execution of `recvmmsg`. The `RIP` being in user space is likely an artifact of how the crash was captured or a specific type of fault (e.g., `IRET` fault or similar). However, the call trace is the most reliable part. The kernel crashed *inside* `tcp_recvmsg`. * *Wait, another possibility*: The `RIP` is `0x7faeb6363db9`. The `CR2` is `0x7f1155bf2304`. The `CR0` is `0x80050033`. * Let's look at the `Call Trace` again. It ends at `tcp_recvmsg_locked`. This function accesses socket buffers. * If the `RIP` is truly in user space, it might be that the kernel returned to user space with a bad state, or the dump is from a tool like `perf` or `bpf` that captured the context. * *Actually*, there is a known issue where if a kernel panic happens, the `RIP` is kernel space. If `RIP` is user space, it's usually a user-space crash. * *Let's look at the `RSP`*: `002b:0x7faeb6363db9`? No, `RSP: 002b:00007f1155bf22f0`. `002b` is the user-space data segment. * This dump looks like it was captured *from user space* or the context is mixed. * *However*, the `Call Trace` is undeniably kernel code. * *Conclusion*: The kernel crashed inside `tcp_recvmsg`. The user-space registers are shown because the crash happened during a syscall. The `RIP` being user-space might be a display artifact or a specific fault type (like a return-to-user fault). The core issue is in `tcp_recvmsg`.
4. **Identify the Bug**: * The crash is in `tcp_recvmsg`. This function handles receiving data on a TCP socket. * Common bugs here involve: * Null pointer dereference (e.g., `sk->sk_prot` is null, or `tp` is null). * Use-after-free (accessing a socket that has been freed). * Race condition (concurrent access to socket state). * Memory corruption. * Without a specific "BUG:" message or "Call Trace" showing the exact line, we have to infer. * The `CR2` value `0x7f1155bf2304` is the address that caused the fault. If this is a null pointer dereference, `CR2` would be 0. It's not. It's a specific user-space address. * *Wait*, if `CR2` is a user-space address, and the crash is in the kernel, this implies the kernel tried to access a user-space address and failed? Or the kernel accessed a kernel address that happens to look like this? * Actually, `CR2` is the faulting linear address. If the kernel is executing, it should be accessing kernel addresses. If `CR2` is a user address, it might mean the kernel was in user mode (which it shouldn't be) or it's a specific type of access (e.g., `copy_from_user` failing, but that usually doesn't crash the kernel, it returns an error). * *Re-evaluating the `RIP`*: `0x7faeb6363db9`. This is the address of the instruction that caused the fault. If this is in user space, the CPU was in user mode. But the `Call Trace` is kernel. This is a contradiction. * *Resolution*: This is likely a **KASAN** or **KCSAN** report, or a crash dump from a tool that captures the user context. Or, more likely, the `RIP` is actually the user-space instruction pointer *at the time of the syscall*, and the crash happened later in the kernel, but the dump format is showing the user `RIP`. * *However*, the most standard interpretation is: The kernel crashed in `tcp_recvmsg`. The `CR2` is the address that caused the page fault. If `CR2` is a user address, it might be that the kernel was trying to access user memory (e.g., in `copy_to_user`) and the user memory was invalid. But `tcp_recvmsg` uses `skb_copy_datagram_iter` which handles this safely. * *Alternative*: The `CR2` is a kernel address that is being interpreted as user space? No, `0x7f...` is clearly user space. * *Hypothesis*: The crash is a **Use-After-Free** or **Null Pointer Dereference** in `tcp_recvmsg`. The `CR2` might be a red herring or related to the user-space buffer passed to `recvmmsg`. * *Let's look at the `Call Trace` again*: `tcp_recvmsg_locked` -> `tcp_recvmsg` -> `inet_recvmsg` -> `sock_recvmsg` -> `sys_recvmmsg`. * This is a standard receive path. * *Common Bug*: A race condition where the socket is closed/freed while `tcp
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