CVE-2026-31423net/sched: sch_hfsc: fix divide-by-zero in rtsc_min()

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ad8e8fec40290a8c8cf145c0deaadf76f80c5163
• https://git.kernel.org/stable/c/ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f
• https://git.kernel.org/stable/c/25b6821884713a31e2b49fb67b0ebd765b33e0a9
• https://git.kernel.org/stable/c/c56f78614e7781aaceca9bd3cb2128bf7d45c3bd
• https://git.kernel.org/stable/c/b9e6431cbea8bb1fae8069ed099b4ee100499835
• https://git.kernel.org/stable/c/17c1b9807b8a67d676b6dcf749ee932ebaa7f568
• https://git.kernel.org/stable/c/d0aefec1b1a1ba2c1d251028dc2c4e5b4ce1fea5
• https://git.kernel.org/stable/c/4576100b8cd03118267513cafacde164b498b322
• https://cert-portal.siemens.com/productcert/html/ssa-082556.html
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html