CVE-2023-53192

In the Linux kernel, the following vulnerability has been resolved:

vxlan: Fix nexthop hash size

The nexthop code expects a 31 bit hash, such as what is returned by fib_multipath_hash() and rt6_multipath_hash(). Passing the 32 bit hash returned by skb_get_hash() can lead to problems related to the fact that int hash is a negative number when the MSB is set.

In the case of hash threshold nexthop groups, nexthop_select_path_hthr() will disproportionately select the first nexthop group entry. In the case of resilient nexthop groups, nexthop_select_path_res() may do an out of bounds access in nh_buckets[], for example: hash = -912054133 num_nh_buckets = 2 bucket_index = 65535

which leads to the following panic:

BUG: unable to handle page fault for address: ffffc900025910c8 PGD 100000067 P4D 100000067 PUD 10026b067 PMD 0 Oops: 0002 [#1] PREEMPT SMP KASAN NOPTI CPU: 4 PID: 856 Comm: kworker/4:3 Not tainted 6.5.0-rc2+ #34 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Workqueue: ipv6_addrconf addrconf_dad_work RIP: 0010:nexthop_select_path+0x197/0xbf0 Code: c1 e4 05 be 08 00 00 00 4c 8b 35 a4 14 7e 01 4e 8d 6c 25 00 4a 8d 7c 25 08 48 01 dd e8 c2 25 15 ff 49 8d 7d 08 e8 39 13 15 ff <4d> 89 75 08 48 89 ef e8 7d 12 15 ff 48 8b 5d 00 e8 14 55 2f 00 85 RSP: 0018:ffff88810c36f260 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 00000000002000c0 RCX: ffffffffaf02dd77 RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffffc900025910c8 RBP: ffffc900025910c0 R08: 0000000000000001 R09: fffff520004b2219 R10: ffffc900025910cf R11: 31392d2068736168 R12: 00000000002000c0 R13: ffffc900025910c0 R14: 00000000fffef608 R15: ffff88811840e900 FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffc900025910c8 CR3: 0000000129d00000 CR4: 0000000000750ee0 PKRU: 55555554 Call Trace: ? __die+0x23/0x70 ? page_fault_oops+0x1ee/0x5c0 ? __pfx_is_prefetch.constprop.0+0x10/0x10 ? __pfx_page_fault_oops+0x10/0x10 ? search_bpf_extables+0xfe/0x1c0 ? fixup_exception+0x3b/0x470 ? exc_page_fault+0xf6/0x110 ? asm_exc_page_fault+0x26/0x30 ? nexthop_select_path+0x197/0xbf0 ? nexthop_select_path+0x197/0xbf0 ? lock_is_held_type+0xe7/0x140 vxlan_xmit+0x5b2/0x2340 ? __lock_acquire+0x92b/0x3370 ? __pfx_vxlan_xmit+0x10/0x10 ? __pfx___lock_acquire+0x10/0x10 ? __pfx_register_lock_class+0x10/0x10 ? skb_network_protocol+0xce/0x2d0 ? dev_hard_start_xmit+0xca/0x350 ? __pfx_vxlan_xmit+0x10/0x10 dev_hard_start_xmit+0xca/0x350 __dev_queue_xmit+0x513/0x1e20 ? __pfx___dev_queue_xmit+0x10/0x10 ? __pfx_lock_release+0x10/0x10 ? mark_held_locks+0x44/0x90 ? skb_push+0x4c/0x80 ? eth_header+0x81/0xe0 ? __pfx_eth_header+0x10/0x10 ? neigh_resolve_output+0x215/0x310 ? ip6_finish_output2+0x2ba/0xc90 ip6_finish_output2+0x2ba/0xc90 ? lock_release+0x236/0x3e0 ? ip6_mtu+0xbb/0x240 ? __pfx_ip6_finish_output2+0x10/0x10 ? find_held_lock+0x83/0xa0 ? lock_is_held_type+0xe7/0x140 ip6_finish_output+0x1ee/0x780 ip6_output+0x138/0x460 ? __pfx_ip6_output+0x10/0x10 ? __pfx___lock_acquire+0x10/0x10 ? __pfx_ip6_finish_output+0x10/0x10 NF_HOOK.constprop.0+0xc0/0x420 ? __pfx_NF_HOOK.constprop.0+0x10/0x10 ? ndisc_send_skb+0x2c0/0x960 ? __pfx_lock_release+0x10/0x10 ? __local_bh_enable_ip+0x93/0x110 ? lock_is_held_type+0xe7/0x140 ndisc_send_skb+0x4be/0x960 ? __pfx_ndisc_send_skb+0x10/0x10 ? mark_held_locks+0x65/0x90 ? find_held_lock+0x83/0xa0 ndisc_send_ns+0xb0/0x110 ? __pfx_ndisc_send_ns+0x10/0x10 addrconf_dad_work+0x631/0x8e0 ? lock_acquire+0x180/0x3f0 ? __pfx_addrconf_dad_work+0x10/0x10 ? mark_held_locks+0x24/0x90 process_one_work+0x582/0x9c0 ? __pfx_process_one_work+0x10/0x10 ? __pfx_do_raw_spin_lock+0x10/0x10 ? mark_held_locks+0x24/0x90 worker_thread+0x93/0x630 ? __kthread_parkme+0xdc/0x100 ? __pfx_worker_thread+0x10/0x10 kthread+0x1a5/0x1e0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x34/0x60

—truncated—

Weakness

The product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array.

Affected Software

Potential Mitigations

• For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
• Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, Ada allows the programmer to constrain the values of a variable and languages such as Java and Ruby will allow the programmer to handle exceptions when an out-of-bounds index is accessed.
• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.
• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.
• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.
• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].
• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• When accessing a user-controlled array index, use a stringent range of values that are within the target array. Make sure that you do not allow negative values to be used. That is, verify the minimum as well as the maximum of the range of acceptable values.
• Run the code in a “jail” or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.
• OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.
• This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.
• Be careful to avoid CWE-243 and other weaknesses related to jails.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/100.html

References

• https://git.kernel.org/stable/c/0756384fb1bd38adb2ebcfd1307422f433a1d772
• https://git.kernel.org/stable/c/23c195ce6f4aec86e1c9e1ea1c800381c4b465c7
• https://git.kernel.org/stable/c/32ef2c0c6cf11a076f0280a7866b9abc47821e19
• https://git.kernel.org/stable/c/7b8717658dff8b471cbfc124bf9b5ca4229579ed
• https://git.kernel.org/stable/c/c650597647ecb318d02372277bdfd866c6829f78