Bugzilla – Bug 1220951
VUL-0: REJECTED: CVE-2021-47085: kernel: hamradio: improve the incomplete fix to avoid NPD
Last modified: 2024-05-31 13:11:31 UTC
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. References: http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-47085 https://www.cve.org/CVERecord?id=CVE-2021-47085 https://lore.kernel.org/linux-cve-announce/2024030455-CVE-2021-47085-3c44@gregkh/ Patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b2f37aead1b8
Already fixed: -cve/linux-5.14 -stable -SLE15-SP6 @kernel-team please add the CVE reference. cve/linux-4.4, cve/linux-4.12, cve/linux-5.3 not affected because CONFIG_MKISS is not set.
REJECTED: https://lore.kernel.org/linux-cve-announce/2024031945-REJECTED-6d41@gregkh/T/#u
(In reply to Robert Frohl from comment #2) > REJECTED: > > https://lore.kernel.org/linux-cve-announce/2024031945-REJECTED-6d41@gregkh/T/ > #u Because CVE-2021-47085 be rejected by upstream. Reset assigner.
All done, closing.