On 19/09/2025 07:45, Deepak Sharma wrote:

Syzbot reported an uninit-value bug at nci_init_req for commit
5aca7966d2a7 ("Merge tag 'perf-tools-fixes-for-v6.17-2025-09-16'..).

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: 6a2968aaf50c ("NFC: basic NCI protocol implementation)
Tested-by: syzbot+740e04c2a93467a0f8c8@syzkaller.appspotmail.com
Signed-off-by: Deepak Sharma <redacted>
---
v3:
  - Move the checks inside the packet data handlers
  - Improvements to the commit message

v2:
  - Fix the release of skb in case of the early return

v1:
  - Add checks in `nci_ntf_packet` on the skb->len and do early return
    on failure

LGTM,
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>