CVE-2026-48065: pam_usb: Unchecked integer multiplication before xmalloc() in conf.c allows heap-based buffer overflow on 32-bit targets

pamusb provides hardware authentication for Linux using ordinary removable media. Prior to 0.9.1, src/conf.c allocates heap memory proportional to ndevices, a count derived from libxml2 XPath evaluation of the config file, without first enforcing an upper bound. On 32-bit targets (armv7l, i686 -- both listed in the project Makefile), the multiplication ndevices sizeof(tpusbdevice) wraps around sizet, causing xmalloc() to receive a very small size. Because xmalloc() only calls abort() on NULL return, a small-but-non-NULL allocation is accepted, and subsequent array writes overflow the heap. This vulnerability is fixed in 0.9.1.