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CVE-2026-31700 In the Linux kernel, the following vulnerability has been resolved: net/packet: fix TOCTOU race on mmap'd vnet_hdr in…

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.

Affected products and versions

Product Affected versions Fixed in
Linux 7.1 earliest → < 7.1 7.1
Linux 7.0 earliest → < 7.0.2 7.0.2
Linux 6.18 earliest → < 6.18.25 6.18.25
Linux 6.12 earliest → < 6.12.84 6.12.84
Linux 6.6 earliest → < 6.6.136 6.6.136
Linux 6.1 earliest → < 6.1.176 6.1.176
Linux 5.15 earliest → < 5.15.210 5.15.210
Linux 5.10 earliest → < 5.10.259 5.10.259
Linux 4.6 No fix stated
Show the 4 other branches
Product Affected versions Fixed in
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP 3.1 3.1.7 → latest No fix stated
SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP 3.1 3.1.7 → latest No fix stated
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP 3.1 3.1.7 → latest No fix stated
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem Versions not published

References

Timeline

  1. Published
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