| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2021-47584: iocost: Fix divide-by-zero on donation from low hweight cgroup |
| |
| Description |
| =========== |
| |
| 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. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47584 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.10 with commit f1de2439ec43b74764f2a26e3a310b24407e3bde and fixed in 5.10.88 with commit a7c80674538f15f85d68138240aae440b8039519 |
| Issue introduced in 5.10 with commit f1de2439ec43b74764f2a26e3a310b24407e3bde and fixed in 5.15.11 with commit 3a1a4eb574178c21241a6200f4785572e661c472 |
| Issue introduced in 5.10 with commit f1de2439ec43b74764f2a26e3a310b24407e3bde and fixed in 5.16 with commit edaa26334c117a584add6053f48d63a988d25a6e |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2021-47584 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| block/blk-iocost.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/a7c80674538f15f85d68138240aae440b8039519 |
| https://git.kernel.org/stable/c/3a1a4eb574178c21241a6200f4785572e661c472 |
| https://git.kernel.org/stable/c/edaa26334c117a584add6053f48d63a988d25a6e |
