Description (CNA)
In the Linux kernel, the following vulnerability has been resolved: net: ipv4: Fix UDP length overflow with PMTU discover and big MTU This commit bounds cork->base.fragsize to IP_MAX_MTU to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IP_MTU_DISCOVER is set to IP_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU. Steps to reproduce: 1. Set device MTU bigger than IP_MAX_MTU + 20. cork->base.fragsize will be set to that MTU in ip_setup_cork. 2. Set IP_MTU_DISCOVER to IP_PMTUDISC_PROBE. It lets maxnonfragsize be set to device MTU (cork->fragsize) in __ip_append_data, rather than to IP_MAX_MTU. 3. Send 65528 bytes of payload (+8 bytes of UDP header, +20 bytes of IPv4 header). Device MTU allows it (it's only one byte bigger than IP_MAX_MTU + IPv4 header, and the device MTU is bigger than that). 4. The UDP length in the built packet is 65536, which overflows the 16-bit length field and triggers the WARN in udp_set_len_short. Note: IP_PMTUDISC_DO with IPv4 is safe, because ip_dst_mtu_maybe_forward always clamps at IP_MAX_MTU, unlike ip6_dst_mtu_maybe_forward. The Fixes tag points at the first commit where I could reproduce the overflow with IPv4 and IP_PMTUDISC_PROBE.
Affected (CNA)
| Vendor / product | Versions |
|---|---|
| Linux / Linux | affected daba287b299ec7a2c61ae3a714920e90e8396ad5 before 83fedc4741210f75be8ca5b487985a242bf6f18d; affected daba287b299ec7a2c61ae3a714920e90e8396ad5 before 81f540827d243b8dad76c1f44e70ea31719f393c; affected daba287b299ec7a2c61ae3a714920e90e8396ad5 before b83641e0ab8b20eefcc4cdc5a059f897375291a2 |
| Linux / Linux | affected 3.13; unaffected 0 before 3.13; unaffected 6.18.53 through 6.18.*; unaffected 7.2.7 through 7.2.*; unaffected 7.3 through * |
CWE
No CWE identifiers supplied.