| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-53044: net/sched: sch_api: fix xa_insert() error path in tcf_block_get_ext() |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| net/sched: sch_api: fix xa_insert() error path in tcf_block_get_ext() |
| |
| This command: |
| |
| $ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact |
| Error: block dev insert failed: -EBUSY. |
| |
| fails because user space requests the same block index to be set for |
| both ingress and egress. |
| |
| [ side note, I don't think it even failed prior to commit 913b47d3424e |
| ("net/sched: Introduce tc block netdev tracking infra"), because this |
| is a command from an old set of notes of mine which used to work, but |
| alas, I did not scientifically bisect this ] |
| |
| The problem is not that it fails, but rather, that the second time |
| around, it fails differently (and irrecoverably): |
| |
| $ tc qdisc replace dev eth0 ingress_block 1 egress_block 1 clsact |
| Error: dsa_core: Flow block cb is busy. |
| |
| [ another note: the extack is added by me for illustration purposes. |
| the context of the problem is that clsact_init() obtains the same |
| &q->ingress_block pointer as &q->egress_block, and since we call |
| tcf_block_get_ext() on both of them, "dev" will be added to the |
| block->ports xarray twice, thus failing the operation: once through |
| the ingress block pointer, and once again through the egress block |
| pointer. the problem itself is that when xa_insert() fails, we have |
| emitted a FLOW_BLOCK_BIND command through ndo_setup_tc(), but the |
| offload never sees a corresponding FLOW_BLOCK_UNBIND. ] |
| |
| Even correcting the bad user input, we still cannot recover: |
| |
| $ tc qdisc replace dev swp3 ingress_block 1 egress_block 2 clsact |
| Error: dsa_core: Flow block cb is busy. |
| |
| Basically the only way to recover is to reboot the system, or unbind and |
| rebind the net device driver. |
| |
| To fix the bug, we need to fill the correct error teardown path which |
| was missed during code movement, and call tcf_block_offload_unbind() |
| when xa_insert() fails. |
| |
| [ last note, fundamentally I blame the label naming convention in |
| tcf_block_get_ext() for the bug. The labels should be named after what |
| they do, not after the error path that jumps to them. This way, it is |
| obviously wrong that two labels pointing to the same code mean |
| something is wrong, and checking the code correctness at the goto site |
| is also easier ] |
| |
| The Linux kernel CVE team has assigned CVE-2024-53044 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.8 with commit 94e2557d086ad831027c54bc9c2130d337c72814 and fixed in 6.11.7 with commit 8966eb69a143b1c032365fe84f2815f3c46f2590 |
| Issue introduced in 6.8 with commit 94e2557d086ad831027c54bc9c2130d337c72814 and fixed in 6.12 with commit a13e690191eafc154b3f60afe9ce35aa9b9128b4 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2024-53044 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| net/sched/cls_api.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/8966eb69a143b1c032365fe84f2815f3c46f2590 |
| https://git.kernel.org/stable/c/a13e690191eafc154b3f60afe9ce35aa9b9128b4 |
