In the Linux kernel, the following vulnerability has been resolved:
iocost: Fix divide-by-zero on donation from low hweight cgroup
The donation calculation logic assumes that the donor has non-zero
after-donation hweight, so the lowest active hweight a donating cgroup can
have is 2 so that it can donate 1 while keeping the other 1 for itself.
Earlier, we only donated from cgroups with sizable surpluses so this
condition was always true. However, with the precise donation algorithm
implemented, f1de2439ec43 (“blk-iocost: revamp donation amount
determination”) made the donation amount calculation exact enabling even
low
hweight cgroups to donate.
This means that in rare occasions, a cgroup with active hweight of 1 can
enter donation calculation triggering the following warning and then a
divide-by-zero oops.
WARNING: CPU: 4 PID: 0 at block/blk-iocost.c:1928
transfer_surpluses.cold+0x0/0x53 [884/94867]
…
RIP: 0010:transfer_surpluses.cold+0x0/0x53
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 <0f> 0b 48 c7 c7
30 da ab b5 e8 71 3f fe ff 4c 89 e8 4d 85 ed 74 0
4
…
Call Trace:
<IRQ>
ioc_timer_fn+0x1043/0x1390
call_timer_fn+0xa1/0x2c0
__run_timers.part.0+0x1ec/0x2e0
run_timer_softirq+0x35/0x70
…
iocg: invalid donation weights in /a/b: active=1 donating=1 after=0
Fix it by excluding cgroups w/ active hweight < 2 from donating. Excluding
these extreme low hweight donations shouldn’t affect work conservation in
any meaningful way.
OS | Version | Architecture | Package | Version | Filename |
---|---|---|---|---|---|
ubuntu | 18.04 | noarch | linux | < any | UNKNOWN |
ubuntu | 20.04 | noarch | linux | < any | UNKNOWN |
ubuntu | 22.04 | noarch | linux | < any | UNKNOWN |
ubuntu | 23.10 | noarch | linux | < any | UNKNOWN |
ubuntu | 24.04 | noarch | linux | < any | UNKNOWN |
ubuntu | 14.04 | noarch | linux | < any | UNKNOWN |
ubuntu | 16.04 | noarch | linux | < any | UNKNOWN |
ubuntu | 18.04 | noarch | linux-aws | < any | UNKNOWN |
ubuntu | 20.04 | noarch | linux-aws | < any | UNKNOWN |
ubuntu | 22.04 | noarch | linux-aws | < any | UNKNOWN |
git.kernel.org/linus/edaa26334c117a584add6053f48d63a988d25a6e (5.16-rc6)
git.kernel.org/stable/c/3a1a4eb574178c21241a6200f4785572e661c472
git.kernel.org/stable/c/a7c80674538f15f85d68138240aae440b8039519
git.kernel.org/stable/c/edaa26334c117a584add6053f48d63a988d25a6e
launchpad.net/bugs/cve/CVE-2021-47584
nvd.nist.gov/vuln/detail/CVE-2021-47584
security-tracker.debian.org/tracker/CVE-2021-47584
www.cve.org/CVERecord?id=CVE-2021-47584