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

Overview

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

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ad8e8fec40290a8c8cf145c0deaadf76f80c5163
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ab1ff5890c7354afc7be56502fcfbd61f3b7ae4f
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 25b6821884713a31e2b49fb67b0ebd765b33e0a9
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c56f78614e7781aaceca9bd3cb2128bf7d45c3bd
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b9e6431cbea8bb1fae8069ed099b4ee100499835
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 17c1b9807b8a67d676b6dcf749ee932ebaa7f568
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < d0aefec1b1a1ba2c1d251028dc2c4e5b4ce1fea5
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 4576100b8cd03118267513cafacde164b498b322
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.