| From bippy-4986f5686161 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-2021-47084: hamradio: defer ax25 kfree after unregister_netdev |
| Message-Id: <2024030455-CVE-2021-47084-4984@gregkh> |
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| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| hamradio: defer ax25 kfree after unregister_netdev |
| |
| There is a possible race condition (use-after-free) like below |
| |
| (USE) | (FREE) |
| ax25_sendmsg | |
| ax25_queue_xmit | |
| dev_queue_xmit | |
| __dev_queue_xmit | |
| __dev_xmit_skb | |
| sch_direct_xmit | ... |
| xmit_one | |
| netdev_start_xmit | tty_ldisc_kill |
| __netdev_start_xmit | mkiss_close |
| ax_xmit | kfree |
| ax_encaps | |
| | |
| |
| Even though there are two synchronization primitives before the kfree: |
| 1. wait_for_completion(&ax->dead). This can prevent the race with |
| routines from mkiss_ioctl. However, it cannot stop the routine coming |
| from upper layer, i.e., the ax25_sendmsg. |
| |
| 2. netif_stop_queue(ax->dev). It seems that this line of code aims to |
| halt the transmit queue but it fails to stop the routine that already |
| being xmit. |
| |
| This patch reorder the kfree after the unregister_netdev to avoid the |
| possible UAF as the unregister_netdev() is well synchronized and won't |
| return if there is a running routine. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47084 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Fixed in 4.4.297 with commit b5b193d0c671 |
| Fixed in 4.9.295 with commit 8a1a314965a1 |
| Fixed in 4.14.260 with commit eaa816a86e62 |
| Fixed in 4.19.223 with commit 896193a02a29 |
| Fixed in 5.4.169 with commit ef5f7bfa19e3 |
| Fixed in 5.10.89 with commit 450121075a6a |
| Fixed in 5.15.12 with commit cb6c99aedd2c |
| Fixed in 5.16 with commit 3e0588c291d6 |
| |
| Please see https://www.kernel.org or 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-2021-47084 |
| 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/hamradio/mkiss.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/b5b193d0c67180fefdc664650138e3b7959df615 |
| https://git.kernel.org/stable/c/8a1a314965a17c62084a056b4f2cb7a770854c90 |
| https://git.kernel.org/stable/c/eaa816a86e629cbcc0a94f38391fee09231628c7 |
| https://git.kernel.org/stable/c/896193a02a2981e60c40d4614fd095ce92135ccd |
| https://git.kernel.org/stable/c/ef5f7bfa19e3fc366f4c6d1a841ceaddf7a9f5d4 |
| https://git.kernel.org/stable/c/450121075a6a6f1d50f97225d3396315309d61a1 |
| https://git.kernel.org/stable/c/cb6c99aedd2c843056a598a8907a6128cb07603b |
| https://git.kernel.org/stable/c/3e0588c291d6ce225f2b891753ca41d45ba42469 |
