Bug 2457839 (CVE-2026-31423)

Summary: CVE-2026-31423 kernel: net/sched: sch_hfsc: fix divide-by-zero in rtsc_min()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel's Hierarchical Fair Service Curve (HFSC) network scheduler. When processing specific large input values, a calculation error can cause a variable to be truncated to zero. This zero value is then used as a divisor, leading to a divide-by-zero error and a system crash, resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-04-13 14:02:33 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_hfsc: fix divide-by-zero in rtsc_min()

m2sm() converts a u32 slope to a u64 scaled value.  For large inputs
(e.g. m1=4000000000), the result can reach 2^32.  rtsc_min() stores
the difference of two such u64 values in a u32 variable `dsm` and
uses it as a divisor.  When the difference is exactly 2^32 the
truncation yields zero, causing a divide-by-zero oops in the
concave-curve intersection path:

  Oops: divide error: 0000
  RIP: 0010:rtsc_min (net/sched/sch_hfsc.c:601)
  Call Trace:
   init_ed (net/sched/sch_hfsc.c:629)
   hfsc_enqueue (net/sched/sch_hfsc.c:1569)
   [...]

Widen `dsm` to u64 and replace do_div() with div64_u64() so the full
difference is preserved.
Comment 1 Keith Grant 2026-04-13 17:06:06 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026041356-CVE-2026-31423-ed66@gregkh/T