Re: [PATCH] net: nfc: nci: fix for UBSAN: shift-out-of-bounds in nci_activate_target

Krzysztof Kozlowski
2023-04-19T08:26:38Z

On 19/04/2023 03:16, Anup Sharma wrote:
> syzbot found UBSAN: shift-out-of-bounds in nci_activate_target [1],
> when nci_target->supported_protocols is bigger than UNIT_MAX,

UINT_MAX?

> where supported_protocols is unsigned 32-bit interger type.

integer?

>
> 32 is the maximum allowed for supported_protocols. Added a check
> for it.
>
> [1] UBSAN: shift-out-of-bounds in net/nfc/nci/core.c:912:45
> shift exponent 4294967071 is too large for 32-bit type 'int'
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
> ubsan_epilogue lib/ubsan.c:217 [inline]
> __ubsan_handle_shift_out_of_bounds+0x221/0x5a0 lib/ubsan.c:387
> nci_activate_target.cold+0x1a/0x1f net/nfc/nci/core.c:912
> nfc_activate_target+0x1f8/0x4c0 net/nfc/core.c:420
> nfc_genl_activate_target+0x1f3/0x290 net/nfc/netlink.c:900
> genl_family_rcv_msg_doit.isra.0+0x1e6/0x2d0 net/netlink/genetlink.c:968
> genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline]
>
> Reported-by: syzbot+0839b78e119aae1fec78@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=19cf2724120ef8c51c8d2566df0cc34617188433
>
> Signed-off-by: anupsharma <anupnewsmail@gmail.com>
> ---
> net/nfc/nci/core.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
> index fff755dde30d..e9d968bd1cd9 100644
> --- a/net/nfc/nci/core.c
> +++ b/net/nfc/nci/core.c
> @@ -908,6 +908,11 @@ static int nci_activate_target(struct nfc_dev *nfc_dev,
> pr_err("unable to find the selected target\n");
> return -EINVAL;
> }
> +
> + if (nci_target->supported_protocols >= 32) {

I don't think it makes any sense. How do you protect from UBSAN reported
shift? Why supported_protocols cannot be 33? You are not shifting the
supported_protocols...

> + pr_err("Too many supported protocol by the device\n");
> + return -EINVAL;

I am pretty sure that you broke now NFC. Test the patches first and
share your test scenario.

> + }
>
> if (!(nci_target->supported_protocols & (1 << protocol))) {

Best regards,
Krzysztof