CVE-2026-31700 - net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

CVE-2026-31700 - net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

https://cvefeed.io/rssfeed/latest.atom / Fri, 05/01/2026 - 17:21
CVE ID :CVE-2026-31700
Published : May 1, 2026, 1:56 p.m. | 19 minutes ago
Description :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.
Severity: 0.0 | NA
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