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Syzbot reported an uninitialized value bug in nci_init_req, which was introduced by commit5aca7966d2("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). Reported-by: syzbot+740e04c2a93467a0f8c8@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=740e04c2a93467a0f8c8 Fixes:6a2968aaf5("NFC: basic NCI protocol implementation") Tested-by: syzbot+740e04c2a93467a0f8c8@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Deepak Sharma <deepak.sharma.472935@gmail.com> Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev> Link: https://patch.msgid.link/20250925132846.213425-1-deepak.sharma.472935@gmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>