CVE-2023-54206 in Linux
Riassunto
di VulDB • 02/07/2026
Based on the kernel stack trace provided, here is an analysis of the issue:
### **Summary** The system experienced a crash (likely a `BUG()` or panic) while attempting to **delete a traffic control filter (`tc del tfilter`)** using the **flower classifier** (`cls_flower`). The crash occurred during the dump/dump-key operation, specifically in `fl_dump`, which is called from `tcf_fill_node`.
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### **Key Stack Trace Analysis**
1. **Triggering Event**: * `rtnetlink_rcv_msg` → `tc_del_tfilter`: A user-space tool (like `ip route` or `tc`) sent a netlink message to delete a traffic control filter. * This is handled by the kernel's networking subsystem via rtnetlink.
2. **Crash Location**: * `tcf_fill_node`: The kernel was preparing data to send back to user-space (likely as part of error reporting or state dump during deletion). * `fl_dump` (`[cls_flower]`): This is the specific function in the flower classifier that dumps filter details. It calls helper functions like `nla_put` and potentially accesses complex structures.
3. **Suspected Cause**: * The presence of `? fl_dump_key_options.part.0+0xea0/0xea0 [cls_flower]` earlier in the truncated part (and its absence here, but implied by context) suggests that while dumping key options for a flower filter, something went wrong.
* Common causes for crashes in `fl_dump`: - **Use-After-Free**: The filter structure was partially freed or corrupted before being fully dumped. - **Null Pointer Dereference**: Accessing a member of the filter's keys (e.g., match fields) that is NULL due to malformed configuration or race condition. - **Invalid Memory Access**: Corrupted memory in the `sk_buff` or netlink attributes (`nla_put`).
4. **Context Clues**: - The stack shows calls to `_raw_spin_lock`, `_raw_read_lock_irq`, and `security_capable`, indicating this happened under lock protection, but a bug still occurred (e.g., locking order violation leading to deadlock? Unlikely for a crash; more likely data corruption). - The function `fl_dump` is known in older kernels to have issues with certain complex flower filters or when hardware offload state is inconsistent.
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### **Recommended Actions**
1. **Check Kernel Version**: This looks like an issue present in some versions of the Linux kernel (particularly around v4.x–v5.x). Check if your kernel version has known bugs related to `cls_flower` or `tc_del_tfilter`. Look for commits fixing crashes in `fl_dump` or flower classifier.
2. **Reproduce with Minimal Configuration**: - Try to reproduce the crash by deleting a simple flower filter: ```bash tc qdisc add dev eth0 handle ffff: ingress tc filter add dev eth0 parent ffff: protocol ip prio 1 u32 match ip src 192.168.1.1/32 action drop # Then delete it tc filter del dev eth0 parent ffff: proto ip handle <handle> ``` - If the crash only happens with complex flower filters (e.g., matching on VLAN, MPLS, or metadata), simplify the rule to isolate.
3. **Check for Hardware Offload Issues**: - Flower classifiers often interact with NIC hardware offloading (`tc flowers ... action mirred egress mirror dev eth1`). If the device doesn't support full offload or has a driver bug, this can cause crashes during filter management. Try disabling offload: ```bash tc qdisc add dev eth0 handle ffff: ingress flower skip_sw # Force software-only if possible ```
4. **Update Kernel/Drivers**: - If you're on an older kernel, consider updating to a newer stable version where `cls_flower` bugs may have been fixed. - Ensure your NIC driver is up-to-date, as hardware offload interactions are common culprits.
5. **Enable Debugging (if possible)**: - Reboot with `slub_debug=O` or enable kernel debugging symbols to get more precise information about the corrupted memory if it happens again. - Check `dmesg` for any preceding warnings like "BUG: unable to handle kernel paging request" or "general protection fault".
6. **Workaround**: If this is a production system and you cannot update immediately, avoid using complex flower filters with hardware offload until the issue is resolved.
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