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22 lines
3.7 KiB
Markdown
22 lines
3.7 KiB
Markdown
### [CVE-2024-56770](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-56770)
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### Description
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In the Linux kernel, the following vulnerability has been resolved:net/sched: netem: account for backlog updates from child qdiscIn general, 'qlen' of any classful qdisc should keep track of thenumber of packets that the qdisc itself and all of its children holds.In case of netem, 'qlen' only accounts for the packets in its internaltfifo. When netem is used with a child qdisc, the child qdisc can use'qdisc_tree_reduce_backlog' to inform its parent, netem, about createdor dropped SKBs. This function updates 'qlen' and the backlog statisticsof netem, but netem does not account for changes made by a child qdisc.'qlen' then indicates the wrong number of packets in the tfifo.If a child qdisc creates new SKBs during enqueue and informs its parentabout this, netem's 'qlen' value is increased. When netem dequeues thenewly created SKBs from the child, the 'qlen' in netem is not updated.If 'qlen' reaches the configured sch->limit, the enqueue function stopsworking, even though the tfifo is not full.Reproduce the bug:Ensure that the sender machine has GSO enabled. Configure netem as rootqdisc and tbf as its child on the outgoing interface of the machineas follows:$ tc qdisc add dev <oif> root handle 1: netem delay 100ms limit 100$ tc qdisc add dev <oif> parent 1:0 tbf rate 50Mbit burst 1542 latency 50msSend bulk TCP traffic out via this interface, e.g., by running an iPerf3client on the machine. Check the qdisc statistics:$ tc -s qdisc show dev <oif>Statistics after 10s of iPerf3 TCP test before the fix (note thatnetem's backlog > limit, netem stopped accepting packets):qdisc netem 1: root refcnt 2 limit 1000 delay 100ms Sent 2767766 bytes 1848 pkt (dropped 652, overlimits 0 requeues 0) backlog 4294528236b 1155p requeues 0qdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms Sent 2767766 bytes 1848 pkt (dropped 327, overlimits 7601 requeues 0) backlog 0b 0p requeues 0Statistics after the fix:qdisc netem 1: root refcnt 2 limit 1000 delay 100ms Sent 37766372 bytes 24974 pkt (dropped 9, overlimits 0 requeues 0) backlog 0b 0p requeues 0qdisc tbf 10: parent 1:1 rate 50Mbit burst 1537b lat 50ms Sent 37766372 bytes 24974 pkt (dropped 327, overlimits 96017 requeues 0) backlog 0b 0p requeues 0tbf segments the GSO SKBs (tbf_segment) and updates the netem's 'qlen'.The interface fully stops transferring packets and "locks". In this case,the child qdisc and tfifo are empty, but 'qlen' indicates the tfifo is atits limit and no more packets are accepted.This patch adds a counter for the entries in the tfifo. Netem's 'qlen' isonly decreased when a packet is returned by its dequeue function, and notduring enqueuing into the child qdisc. External updates to 'qlen' are thusaccounted for and only the behavior of the backlog statistics changes. Asin other qdiscs, 'qlen' then keeps track of how many packets are held innetem and all of its children. As before, sch->limit remains as themaximum number of packets in the tfifo. The same applies to netem'sbacklog statistics.
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### POC
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#### Reference
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No PoCs from references.
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#### Github
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- https://github.com/oogasawa/Utility-security
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- https://github.com/w4zu/Debian_security
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- https://github.com/xairy/linux-kernel-exploitation
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