Bug 2376074 (CVE-2025-38115)

Summary: CVE-2025-38115 kernel: Linux kernel: Local Denial of Service in network scheduler
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel's network scheduler, specifically within the Stochastic Fair Queueing (SFQ) mechanism. A local user could exploit this vulnerability by manipulating network packet queues, leading to an immediate drop of legitimate network traffic. This issue can result in a denial of service (DoS), making the system unresponsive.
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Description OSIDB Bzimport 2025-07-03 09:03:46 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net_sched: sch_sfq: fix a potential crash on gso_skb handling

SFQ has an assumption of always being able to queue at least one packet.

However, after the blamed commit, sch->q.len can be inflated by packets
in sch->gso_skb, and an enqueue() on an empty SFQ qdisc can be followed
by an immediate drop.

Fix sfq_drop() to properly clear q->tail in this situation.


ip netns add lb
ip link add dev to-lb type veth peer name in-lb netns lb
ethtool -K to-lb tso off                 # force qdisc to requeue gso_skb
ip netns exec lb ethtool -K in-lb gro on # enable NAPI
ip link set dev to-lb up
ip -netns lb link set dev in-lb up
ip addr add dev to-lb 192.168.20.1/24
ip -netns lb addr add dev in-lb 192.168.20.2/24
tc qdisc replace dev to-lb root sfq limit 100

ip netns exec lb netserver

netperf -H 192.168.20.2 -l 100 &
netperf -H 192.168.20.2 -l 100 &
netperf -H 192.168.20.2 -l 100 &
netperf -H 192.168.20.2 -l 100 &
Comment 1 Avinash Hanwate 2025-07-03 16:45:10 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025070325-CVE-2025-38115-cce2@gregkh/T