| 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-2021-47396: mac80211-hwsim: fix late beacon hrtimer handling |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| mac80211-hwsim: fix late beacon hrtimer handling |
| |
| Thomas explained in https://lore.kernel.org/r/87mtoeb4hb.ffs@tglx |
| that our handling of the hrtimer here is wrong: If the timer fires |
| late (e.g. due to vCPU scheduling, as reported by Dmitry/syzbot) |
| then it tries to actually rearm the timer at the next deadline, |
| which might be in the past already: |
| |
| 1 2 3 N N+1 |
| | | | ... | | |
| |
| ^ intended to fire here (1) |
| ^ next deadline here (2) |
| ^ actually fired here |
| |
| The next time it fires, it's later, but will still try to schedule |
| for the next deadline (now 3), etc. until it catches up with N, |
| but that might take a long time, causing stalls etc. |
| |
| Now, all of this is simulation, so we just have to fix it, but |
| note that the behaviour is wrong even per spec, since there's no |
| value then in sending all those beacons unaligned - they should be |
| aligned to the TBTT (1, 2, 3, ... in the picture), and if we're a |
| bit (or a lot) late, then just resume at that point. |
| |
| Therefore, change the code to use hrtimer_forward_now() which will |
| ensure that the next firing of the timer would be at N+1 (in the |
| picture), i.e. the next interval point after the current time. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47396 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 3.9 with commit 01e59e467ecf976c782eecd4dc99644802cc60e2 and fixed in 5.4.151 with commit 9bee85de2c8155388c09a2e1530a243ec1c96f05 |
| Issue introduced in 3.9 with commit 01e59e467ecf976c782eecd4dc99644802cc60e2 and fixed in 5.10.71 with commit 2c204cf594df3b9468368dc9d0b24d482d93cda7 |
| Issue introduced in 3.9 with commit 01e59e467ecf976c782eecd4dc99644802cc60e2 and fixed in 5.14.10 with commit ed2adf69e29848d1eb9df99633dde655421c92ed |
| Issue introduced in 3.9 with commit 01e59e467ecf976c782eecd4dc99644802cc60e2 and fixed in 5.15 with commit 313bbd1990b6ddfdaa7da098d0c56b098a833572 |
| |
| 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-2021-47396 |
| 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: |
| drivers/net/wireless/mac80211_hwsim.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/9bee85de2c8155388c09a2e1530a243ec1c96f05 |
| https://git.kernel.org/stable/c/2c204cf594df3b9468368dc9d0b24d482d93cda7 |
| https://git.kernel.org/stable/c/ed2adf69e29848d1eb9df99633dde655421c92ed |
| https://git.kernel.org/stable/c/313bbd1990b6ddfdaa7da098d0c56b098a833572 |
