| 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-2021-47505: aio: fix use-after-free due to missing POLLFREE handling |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| aio: fix use-after-free due to missing POLLFREE handling |
| |
| signalfd_poll() and binder_poll() are special in that they use a |
| waitqueue whose lifetime is the current task, rather than the struct |
| file as is normally the case. This is okay for blocking polls, since a |
| blocking poll occurs within one task; however, non-blocking polls |
| require another solution. This solution is for the queue to be cleared |
| before it is freed, by sending a POLLFREE notification to all waiters. |
| |
| Unfortunately, only eventpoll handles POLLFREE. A second type of |
| non-blocking poll, aio poll, was added in kernel v4.18, and it doesn't |
| handle POLLFREE. This allows a use-after-free to occur if a signalfd or |
| binder fd is polled with aio poll, and the waitqueue gets freed. |
| |
| Fix this by making aio poll handle POLLFREE. |
| |
| A patch by Ramji Jiyani <ramjiyani@google.com> |
| (https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com) |
| tried to do this by making aio_poll_wake() always complete the request |
| inline if POLLFREE is seen. However, that solution had two bugs. |
| First, it introduced a deadlock, as it unconditionally locked the aio |
| context while holding the waitqueue lock, which inverts the normal |
| locking order. Second, it didn't consider that POLLFREE notifications |
| are missed while the request has been temporarily de-queued. |
| |
| The second problem was solved by my previous patch. This patch then |
| properly fixes the use-after-free by handling POLLFREE in a |
| deadlock-free way. It does this by taking advantage of the fact that |
| freeing of the waitqueue is RCU-delayed, similar to what eventpoll does. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47505 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 4.18 with commit 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and fixed in 4.19.221 with commit 321fba81ec034f88aea4898993c1bf15605c023f |
| Issue introduced in 4.18 with commit 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and fixed in 5.4.165 with commit 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f |
| Issue introduced in 4.18 with commit 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and fixed in 5.10.85 with commit 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689 |
| Issue introduced in 4.18 with commit 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and fixed in 5.15.8 with commit 60d311f9e6381d779d7d53371f87285698ecee24 |
| Issue introduced in 4.18 with commit 2c14fa838cbefc23cf1c73ca167ed85b274b2913 and fixed in 5.16 with commit 50252e4b5e989ce64555c7aef7516bdefc2fea72 |
| |
| 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-2021-47505 |
| 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: |
| fs/aio.c |
| include/uapi/asm-generic/poll.h |
| |
| |
| 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/321fba81ec034f88aea4898993c1bf15605c023f |
| https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f |
| https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689 |
| https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24 |
| https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72 |
