In the Linux kernel, the following vulnerability has been resolved: nfc: llcp: avoid userspace overflow on invalid optlen nfc_llcp_getsock

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

nfc: llcp: avoid userspace overflow on invalid optlen

nfc_llcp_getsockopt() casts optval to (u32 __user *) for put_user(), so
the kernel always stores 4 bytes regardless of the caller-supplied
optlen. The existing min_t(u32, len, sizeof(u32)) only clamps the length
reported back to userspace; it does not constrain the store. A call with
optlen < 4 therefore writes past the user buffer, violating the
getsockopt(2) contract for all five supported optnames.

Reject any call with optlen < sizeof(u32) up front. 'len' is int, so a
plain size comparison would promote a negative optlen to size_t and slip
past the check; an explicit 'len < 0' test is added first to catch
negative values before the size compare.