Linux vulnerability

What happened

In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via __packet_snd_vnet_parse() but then re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent userspace thread can modify the vnet_hdr fields between validation and use, bypassing all safety checks. The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr to a stack-local variable. All other vnet_hdr consumers in the kernel (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX path is the only caller of virtio_net_hdr_to_skb() that reads directly from user-controlled shared memory. Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.

Affected versions

Linux: 1d036d25e5609ba73fee6a88db01c306b140d512 through before 0f4c9754956b86de158a4af5278c5cf5bda9439e (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 714aa973da8163925eda7efd49361ccbee21ee46 (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 1490f82353bdabc09265a74e645b07f05cf4188e (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 74e2db36fe50e3ad9d5300d7fd0e6e2a15a6d121 (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 3a1bf9116ea31470b89692585c3910dfe830dcdd (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 28324a3b62d9ce7f9bdd65a8ce63f382041d1b27 (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 48a6ef291a17639e1b6ae0fbe9c8b2bb87d7804b (git); 1d036d25e5609ba73fee6a88db01c306b140d512 through before 2c054e17d9d41f1020376806c7f750834ced4dc5 (git); 4.6; V3.1.6 through before * (custom) Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

• Apply vendor-provided updates or mitigations.
• Review affected product exposure and access logs.