CVE-2021-47584

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> iocost: Fix divide-by-zero on donation from low hweight cgroup<br /> <br /> The donation calculation logic assumes that the donor has non-zero<br /> after-donation hweight, so the lowest active hweight a donating cgroup can<br /> have is 2 so that it can donate 1 while keeping the other 1 for itself.<br /> Earlier, we only donated from cgroups with sizable surpluses so this<br /> condition was always true. However, with the precise donation algorithm<br /> implemented, f1de2439ec43 ("blk-iocost: revamp donation amount<br /> determination") made the donation amount calculation exact enabling even low<br /> hweight cgroups to donate.<br /> <br /> This means that in rare occasions, a cgroup with active hweight of 1 can<br /> enter donation calculation triggering the following warning and then a<br /> divide-by-zero oops.<br /> <br /> WARNING: CPU: 4 PID: 0 at block/blk-iocost.c:1928 transfer_surpluses.cold+0x0/0x53 [884/94867]<br /> ...<br /> RIP: 0010:transfer_surpluses.cold+0x0/0x53<br /> Code: 92 ff 48 c7 c7 28 d1 ab b5 65 48 8b 34 25 00 ae 01 00 48 81 c6 90 06 00 00 e8 8b 3f fe ff 48 c7 c0 ea ff ff ff e9 95 ff 92 ff 0b 48 c7 c7 30 da ab b5 e8 71 3f fe ff 4c 89 e8 4d 85 ed 74 0<br /> 4<br /> ...<br /> Call Trace:<br /> <br /> ioc_timer_fn+0x1043/0x1390<br /> call_timer_fn+0xa1/0x2c0<br /> __run_timers.part.0+0x1ec/0x2e0<br /> run_timer_softirq+0x35/0x70<br /> ...<br /> iocg: invalid donation weights in /a/b: active=1 donating=1 after=0<br /> <br /> Fix it by excluding cgroups w/ active hweight