net: dst_metadata: fix false-positive memcpy overflow in tun_dst_unclone

Summary

In the Linux kernel, the following vulnerability has been resolved: net: dst_metadata: fix false-positive memcpy overflow in tun_dst_unclone kmalloc_flex() in metadata_dst_alloc() sets __counted_by for the structure to the options_len, which is then initialized to zero. Later, we're initializing the structure by copying the tunnel info together with the options, and this triggers a warning for a potential memcpy overflow, since the compiler estimates that the options can't fit into the structure, even though the memory for them is actually allocated. memcpy: detected buffer overflow: 104 byte write of buffer size 96 WARNING: CPU: X PID: Y at lib/string_helpers.c:1036 __fortify_report skb_tunnel_info_unclone+0x179/0x190 geneve_xmit+0x7fe/0xe00 The issue is triggered when built with clang and source fortification. Fix that by doing the copy in two stages: first - the main data with the options_len, then the options. This way the correct length should be known at the time of the copy. It would be better if the options_len never changed after allocation, but the allocation code is a little separate from the initialization and it would be awkward and potentially dangerous to return a struct with options_len set to a non-zero value from the metadata_dst_alloc(). Another option would be to use ip_tunnel_info_opts_set(), but it is doing too many unnecessary operations for the use case here.

Timeline

1. Aug 28, 2026, 6:48 AM UTCCVE published
2. Oct 16, 2026, 7:18 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. Oct 16, 2026, 7:26 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 69050f8d6d075dc01af7a5f2f550a8067510366f · fixed in 7ce31739fe88a558370135db95bbeec1e7ddfc29; From 69050f8d6d075dc01af7a5f2f550a8067510366f · fixed in 4c6d43db2a4d2cef3921e885cf34798f790d34ea

• Linux Linux

  7.0

• KernelLinux

  From 7.0.0 · fixed in 7.1.5

References 2