CVE-2026-90051 (GCVE-0-2026-90051)

Vulnerability from cvelistv5 – Published: 2026-09-17 16:05 – Updated: 2026-09-18 17:52
VLAI
Title
tcp: reject non zerocopy devmem tx
Summary
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.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: bd61848900bff597764238f3a8ec67c815cd316e , < 2151b2bcf6fcec52665f606eed20da068447f0b7 (git)
Affected: bd61848900bff597764238f3a8ec67c815cd316e , < b04326c7927af7048fd4e730f5770cca350d0a60 (git)
Affected: bd61848900bff597764238f3a8ec67c815cd316e , < 125755776bc6d4dd53eaf551c87e3d460625d638 (git)
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Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.18.52 , ≤ 6.18.* (semver)
Unaffected: 7.2.6 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc3 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: reject non zerocopy devmem tx\n\nDevmem tcp tx doesn\u0027t work without zero-copy, however it\u0027s not currently\nenforced if NETIF_F_SG isn\u0027t present. In this case, tcp_sendmsg_locked()\nwill try the copy path and try to copy data from an iovec which consists\nof offsets into the dma-buf and would normally fail. Moreover,\nd9c56501c72fd (\"net: tcp: block mixing readable and unreadable frags\")\nrelies on that and assumes that the devmem binding is present IFF we\u0027re\nusing the zero-copy path, which can be used to mix net-iov and pages in\na single skb, and break invariants. Let\u0027s reject devmem tx without\nzero-copy.\n\nNote, the parameter check the patch is modifying is too loose, we can\ncreate an io_uring request with dmabuf_id and all ZC flags, but which\nwon\u0027t have the binding. We replace it with stricter validation."
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              "value": "AV:L - The triggering input is local sendmsg or io_uring IORING_OP_SENDMSG_ZC into tcp_sendmsg_locked(): SO_ZEROCOPY, MSG_ZEROCOPY, and an SCM_DEVMEM_DMABUF cmsg that sets sockc.dmabuf_id. A remote TCP peer never supplies that cmsg or those send flags; it only receives the resulting segments.\nAC:L - The attacker drives both sendmsg calls: a MSG_ZEROCOPY+SCM_DEVMEM_DMABUF send queues net-iov (unreadable) frags, then a later sendmsg with sockc.dmabuf_id while zc==0 (sk_route_caps lacks NETIF_F_SG, so the copy path runs with binding set) appends pages onto that skb. MSG_MORE retains the write-queue tail; no victim race is required.\nPR:L - NETDEV_CMD_BIND_TX has no GENL_ADMIN_PERM, and SO_ZEROCOPY plus __sock_cmsg_send(SCM_DEVMEM_DMABUF) have no capability checks. An unprivileged user can bind a TX dmabuf and reach the zc/binding check in tcp_sendmsg_locked; any extra CAP_NET_ADMIN is only the user-namespace kind.\nUI:N - The attacker enables SO_ZEROCOPY, binds a dmabuf via netdev-genl NETDEV_CMD_BIND_TX, and issues the crafted sendmsg/IORING_OP_SENDMSG_ZC sequence on their own TCP socket; no victim mount, open, or other interactive action is required.\nS:U - Mixing net_iov and page frags corrupts skb/TX processing on the sending host inside tcp_sendmsg_locked and later frag walkers. It does not cross a VM/guest or IOMMU authority; __skb_frag_dma_map still classifies each frag with skb_frag_is_net_iov.\nC:H - A mixed skb keeps skb-\u003eunreadable from skb_add_rx_frag_netmem while the zc==0 path adds page frags via skb_fill_page_desc. Walkers such as tcp_md5_hash_skb_data use skb_frag_foreach_page/skb_frag_page() on net_iovs (NULL) and kmap that pointer, enabling kernel memory disclosure.\nI:H - Appending sk_page_frag pages onto a net-iov skb via the zc==0 copy path in tcp_sendmsg_locked is frag-type confusion: TX, refcount, and skb_fill_page_desc versus skb_add_rx_frag_netmem cannot treat mixed backing consistently, which yields corrupted skb metadata and write or control-flow primitives.\nA:H - Mixed readable/unreadable frags blow up down the stack: skb_copy_bits/skb_checksum hit WARN_ON_ONCE(!skb_frags_readable), splice hits WARN_ON_ONCE(!skb_frag_page), and kmap of a NULL net_iov page oopses or panics the kernel."
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: reject non zerocopy devmem tx\n\nDevmem tcp tx doesn\u0027t work without zero-copy, however it\u0027s not currently\nenforced if NETIF_F_SG isn\u0027t present. In this case, tcp_sendmsg_locked()\nwill try the copy path and try to copy data from an iovec which consists\nof offsets into the dma-buf and would normally fail. Moreover,\nd9c56501c72fd (\"net: tcp: block mixing readable and unreadable frags\")\nrelies on that and assumes that the devmem binding is present IFF we\u0027re\nusing the zero-copy path, which can be used to mix net-iov and pages in\na single skb, and break invariants. Let\u0027s reject devmem tx without\nzero-copy.\n\nNote, the parameter check the patch is modifying is too loose, we can\ncreate an io_uring request with dmabuf_id and all ZC flags, but which\nwon\u0027t have the binding. We replace it with stricter validation."
          }
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}



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