CVE-2026-31617usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()

Official description

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb() The block_len read from the host-supplied NTB header is checked against ntb_max but has no lower bound. When block_len is smaller than opts->ndp_size, the bounds check of: ndp_index > (block_len - opts->ndp_size) will underflow producing a huge unsigned value that ndp_index can never exceed, defeating the check entirely. The same underflow occurs in the datagram index checks against block_len - opts->dpe_size. With those checks neutered, a malicious USB host can choose ndp_index and datagram offsets that point past the actual transfer, and the skb_put_data() copies adjacent kernel memory into the network skb. Fix this by rejecting block lengths that cannot hold at least the NTB header plus one NDP. This will make block_len - opts->ndp_size and block_len - opts->dpe_size both well-defined. Commit 8d2b1a1ec9f5 ("CDC-NCM: avoid overflow in sanity checking") fixed a related class of issues on the host side of NCM.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/068a7f2749fff6462a0a908ec415b885fe430f50
• https://git.kernel.org/stable/c/1425655c2870054c3ab4712e2b6dbdd331597ada
• https://git.kernel.org/stable/c/8b3b7bd3c02f98634baaf36c7fc7ac915f6517ca
• https://git.kernel.org/stable/c/0f156bb5334e588034ca68ac2ee92b23f66e56e7
• https://git.kernel.org/stable/c/8757a2593631443648218244b9788e193ae0fdc1
• https://git.kernel.org/stable/c/6762f8a95772265dd0c2ffe7f400493f3115b135
• https://git.kernel.org/stable/c/d58ba8f6546232f8414f396c189297dbee03f1a7
• https://git.kernel.org/stable/c/74908b0318d1df1188457040b8714ff4d4b68126
• https://git.kernel.org/stable/c/8f993d30b95dc9557a8a96ceca11abed674c8acb
• https://access.redhat.com/security/cve/CVE-2026-31617 vdb-entry, x_refsource_REDHAT
• RHBZ#2461448 issue-tracking, x_refsource_REDHAT
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31617.json x_sadp-csaf-vex
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html