CVE-2021-47309

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

net: validate lwtstate->data before returning from skb_tunnel_info()

skb_tunnel_info() returns pointer of lwtstate->data as ip_tunnel_info type without validation. lwtstate->data can have various types such as mpls_iptunnel_encap, etc and these are not compatible. So skb_tunnel_info() should validate before returning that pointer.

Splat looks like: BUG: KASAN: slab-out-of-bounds in vxlan_get_route+0x418/0x4b0 [vxlan] Read of size 2 at addr ffff888106ec2698 by task ping/811

CPU: 1 PID: 811 Comm: ping Not tainted 5.13.0+ #1195 Call Trace: dump_stack_lvl+0x56/0x7b print_address_description.constprop.8.cold.13+0x13/0x2ee ? vxlan_get_route+0x418/0x4b0 [vxlan] ? vxlan_get_route+0x418/0x4b0 [vxlan] kasan_report.cold.14+0x83/0xdf ? vxlan_get_route+0x418/0x4b0 [vxlan] vxlan_get_route+0x418/0x4b0 [vxlan] [ … ] vxlan_xmit_one+0x148b/0x32b0 [vxlan] [ … ] vxlan_xmit+0x25c5/0x4780 [vxlan] [ … ] dev_hard_start_xmit+0x1ae/0x6e0 __dev_queue_xmit+0x1f39/0x31a0 [ … ] neigh_xmit+0x2f9/0x940 mpls_xmit+0x911/0x1600 [mpls_iptunnel] lwtunnel_xmit+0x18f/0x450 ip_finish_output2+0x867/0x2040 [ … ]

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• 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.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/2179d96ec702cc33ead02a9ce40ece599b8538c5
• https://git.kernel.org/stable/c/67a9c94317402b826fc3db32afc8f39336803d97
• https://git.kernel.org/stable/c/83bdcfbd968bcc91a0632b7b625e4a9b0cba5e0d
• https://git.kernel.org/stable/c/8aa13a86964cdec4fd969ef677c6614ff068641a
• https://git.kernel.org/stable/c/8bb1589c89e61e3b182dd546f1021928ebb5c2a6
• https://git.kernel.org/stable/c/a915379594f1e045421635c6316d8f3ffa018c58
• https://git.kernel.org/stable/c/b61d327cd3cc5ea591f3bf751dd11e034f388bb5
• https://git.kernel.org/stable/c/e7f3c9df40515a6c6b46f36c4c94cf48a043f887
• https://git.kernel.org/stable/c/2179d96ec702cc33ead02a9ce40ece599b8538c5
• https://git.kernel.org/stable/c/67a9c94317402b826fc3db32afc8f39336803d97
• https://git.kernel.org/stable/c/83bdcfbd968bcc91a0632b7b625e4a9b0cba5e0d
• https://git.kernel.org/stable/c/8aa13a86964cdec4fd969ef677c6614ff068641a
• https://git.kernel.org/stable/c/8bb1589c89e61e3b182dd546f1021928ebb5c2a6
• https://git.kernel.org/stable/c/a915379594f1e045421635c6316d8f3ffa018c58
• https://git.kernel.org/stable/c/b61d327cd3cc5ea591f3bf751dd11e034f388bb5
• https://git.kernel.org/stable/c/e7f3c9df40515a6c6b46f36c4c94cf48a043f887