| 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-2025-21702: pfifo_tail_enqueue: Drop new packet when sch->limit == 0 |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| pfifo_tail_enqueue: Drop new packet when sch->limit == 0 |
| |
| Expected behaviour: |
| In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a |
| packet in scheduler's queue and decrease scheduler's qlen by one. |
| Then, pfifo_tail_enqueue() enqueue new packet and increase |
| scheduler's qlen by one. Finally, pfifo_tail_enqueue() return |
| `NET_XMIT_CN` status code. |
| |
| Weird behaviour: |
| In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a |
| scheduler that has no packet, the 'drop a packet' step will do nothing. |
| This means the scheduler's qlen still has value equal 0. |
| Then, we continue to enqueue new packet and increase scheduler's qlen by |
| one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by |
| one and return `NET_XMIT_CN` status code. |
| |
| The problem is: |
| Let's say we have two qdiscs: Qdisc_A and Qdisc_B. |
| - Qdisc_A's type must have '->graft()' function to create parent/child relationship. |
| Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. |
| - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. |
| - Qdisc_B is configured to have `sch->limit == 0`. |
| - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. |
| |
| Enqueue packet through Qdisc_A will lead to: |
| - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) |
| - Qdisc_B->q.qlen += 1 |
| - pfifo_tail_enqueue() return `NET_XMIT_CN` |
| - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. |
| |
| The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. |
| Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem. |
| This violate the design where parent's qlen should equal to the sum of its childrens'qlen. |
| |
| Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable. |
| |
| The Linux kernel CVE team has assigned CVE-2025-21702 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 5.4.291 with commit 78285b53266d6d51fa4ff504a23df03852eba84e |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 5.10.235 with commit 7a9723ec27aff5674f1fd4934608937f1d650980 |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 5.15.179 with commit a56a6e8589a9b98d8171611fbcc1e45a15fd2455 |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 6.1.130 with commit 020ecb76812a0526f4130ab5aeb6dc7c773e7ab9 |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 6.6.83 with commit 79a955ea4a2e5ddf4a36328959de0de496419888 |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 6.12.14 with commit e40cb34b7f247fe2e366fd192700d1b4f38196ca |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 6.13.3 with commit b6a079c3b6f95378f26e2aeda520cb3176f7067b |
| Issue introduced in 2.6.34 with commit 57dbb2d83d100ea601c54fe129bfde0678db5dee and fixed in 6.14 with commit 647cef20e649c576dff271e018d5d15d998b629d |
| |
| 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-2025-21702 |
| 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/sch_fifo.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/78285b53266d6d51fa4ff504a23df03852eba84e |
| https://git.kernel.org/stable/c/7a9723ec27aff5674f1fd4934608937f1d650980 |
| https://git.kernel.org/stable/c/a56a6e8589a9b98d8171611fbcc1e45a15fd2455 |
| https://git.kernel.org/stable/c/020ecb76812a0526f4130ab5aeb6dc7c773e7ab9 |
| https://git.kernel.org/stable/c/79a955ea4a2e5ddf4a36328959de0de496419888 |
| https://git.kernel.org/stable/c/e40cb34b7f247fe2e366fd192700d1b4f38196ca |
| https://git.kernel.org/stable/c/b6a079c3b6f95378f26e2aeda520cb3176f7067b |
| https://git.kernel.org/stable/c/647cef20e649c576dff271e018d5d15d998b629d |
