Linux Kernel CVE-2025-40043

In the Linux kernel, the following vulnerability has been resolved:

net: nfc: nci: Add parameter validation for packet data

Syzbot reported an uninitialized value bug in nci_init_req, which was introduced by commit 5aca7966d2a7 ("Merge tag 'perf-tools-fixes-for-v6.17-2025-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools").

This bug arises due to very limited and poor input validation that was done at nic_valid_size(). This validation only validates the skb->len (directly reflects size provided at the userspace interface) with the length provided in the buffer itself (interpreted as NCI_HEADER). This leads to the processing of memory content at the address assuming the correct layout per what opcode requires there. This leads to the accesses to buffer of skb_buff->data which is not assigned anything yet.

Following the same silent drop of packets of invalid sizes at nic_valid_size(), add validation of the data in the respective handlers and return error values in case of failure. Release the skb if error values are returned from handlers in nci_nft_packet and effectively do a silent drop

Possible TODO: because we silently drop the packets, the call to nci_request will be waiting for completion of request and will face timeouts. These timeouts can get excessively logged in the dmesg. A proper handling of them may require to export nci_request_cancel (or propagate error handling from the nft packets handlers).

The Linux kernel's NFC NCI subsystem (net/nfc/nci) is affected on builds that enable the NFC stack; the description ties the regression to a merge around the 6.17 development cycle. No CPE strings were provided in the input, so exact affected version ranges are not enumerated here - the six referenced stable-tree commits (git.kernel.org/stable/c/0ba68bea..., 74837bca..., 8fcc7315..., 9c328f54..., bfdda012..., c395d1e5...) indicate the fix was backported across multiple stable branches, implying several maintained series are affected. Consult the kernel.org stable trees and your distribution's advisory to map these commits to the exact released kernel versions you run.