| 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-2021-47085: hamradio: improve the incomplete fix to avoid NPD |
| Message-Id: <2024030455-CVE-2021-47085-3c44@gregkh> |
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| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| hamradio: improve the incomplete fix to avoid NPD |
| |
| The previous commit 3e0588c291d6 ("hamradio: defer ax25 kfree after |
| unregister_netdev") reorder the kfree operations and unregister_netdev |
| operation to prevent UAF. |
| |
| This commit improves the previous one by also deferring the nullify of |
| the ax->tty pointer. Otherwise, a NULL pointer dereference bug occurs. |
| Partial of the stack trace is shown below. |
| |
| BUG: kernel NULL pointer dereference, address: 0000000000000538 |
| RIP: 0010:ax_xmit+0x1f9/0x400 |
| ... |
| Call Trace: |
| dev_hard_start_xmit+0xec/0x320 |
| sch_direct_xmit+0xea/0x240 |
| __qdisc_run+0x166/0x5c0 |
| __dev_queue_xmit+0x2c7/0xaf0 |
| ax25_std_establish_data_link+0x59/0x60 |
| ax25_connect+0x3a0/0x500 |
| ? security_socket_connect+0x2b/0x40 |
| __sys_connect+0x96/0xc0 |
| ? __hrtimer_init+0xc0/0xc0 |
| ? common_nsleep+0x2e/0x50 |
| ? switch_fpu_return+0x139/0x1a0 |
| __x64_sys_connect+0x11/0x20 |
| do_syscall_64+0x33/0x40 |
| entry_SYSCALL_64_after_hwframe+0x44/0xa9 |
| |
| The crash point is shown as below |
| |
| static void ax_encaps(...) { |
| ... |
| set_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags); // ax->tty = NULL! |
| ... |
| } |
| |
| By placing the nullify action after the unregister_netdev, the ax->tty |
| pointer won't be assigned as NULL net_device framework layer is well |
| synchronized. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47085 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Fixed in 4.4.297 with commit 371a874ea06f |
| Fixed in 4.9.295 with commit 83ba6ec97c74 |
| Fixed in 4.14.260 with commit a7b0ae2cc486 |
| Fixed in 4.19.223 with commit b68f41c6320b |
| Fixed in 5.4.169 with commit a5c6a13e9056 |
| Fixed in 5.10.89 with commit 7dd52af1eb57 |
| Fixed in 5.15.12 with commit 03d00f7f1815 |
| Fixed in 5.16 with commit b2f37aead1b8 |
| |
| 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-2021-47085 |
| 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/371a874ea06f147d6ca30be43dad33683965eba6 |
| https://git.kernel.org/stable/c/83ba6ec97c74fb1a60f7779a26b6a94b28741d8a |
| https://git.kernel.org/stable/c/a7b0ae2cc486fcb601f9f9d87d98138cc7b7f7f9 |
| https://git.kernel.org/stable/c/b68f41c6320b2b7fbb54a95f07a69f3dc7e56c59 |
| https://git.kernel.org/stable/c/a5c6a13e9056d87805ba3042c208fbd4164ad22b |
| https://git.kernel.org/stable/c/7dd52af1eb5798f590d9d9e1c56ed8f5744ee0ca |
| https://git.kernel.org/stable/c/03d00f7f1815ec00dab5035851b3de83afd054a8 |
| https://git.kernel.org/stable/c/b2f37aead1b82a770c48b5d583f35ec22aabb61e |
