CVE-2026-90051tcp: reject non zerocopy devmem tx

Official description

In the Linux kernel, the following vulnerability has been resolved: tcp: reject non zerocopy devmem tx Devmem tcp tx doesn't work without zero-copy, however it's not currently enforced if NETIF_F_SG isn't present. In this case, tcp_sendmsg_locked() will try the copy path and try to copy data from an iovec which consists of offsets into the dma-buf and would normally fail. Moreover, d9c56501c72fd ("net: tcp: block mixing readable and unreadable frags") relies on that and assumes that the devmem binding is present IFF we're using the zero-copy path, which can be used to mix net-iov and pages in a single skb, and break invariants. Let's reject devmem tx without zero-copy. Note, the parameter check the patch is modifying is too loose, we can create an io_uring request with dmabuf_id and all ZC flags, but which won't have the binding. We replace it with stricter validation.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/2151b2bcf6fcec52665f606eed20da068447f0b7
• https://git.kernel.org/stable/c/b04326c7927af7048fd4e730f5770cca350d0a60
• https://git.kernel.org/stable/c/125755776bc6d4dd53eaf551c87e3d460625d638