module: fix [e_shstrndx].sh_size=0 OOB access

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

module: fix [e_shstrndx].sh_size=0 OOB access

It is trivial to craft a module to trigger OOB access in this line:

if (info->secstrings[strhdr->sh_size - 1] != '\0') {

BUG: unable to handle page fault for address: ffffc90000aa0fff

PGD 100000067 P4D 100000067 PUD 100066067 PMD 10436f067 PTE 0

Oops: 0000 [#1] PREEMPT SMP PTI

CPU: 7 PID: 1215 Comm: insmod Not tainted 5.18.0-rc5-00007-g9bf578647087-dirty #10

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014

RIP: 0010:load_module+0x19b/0x2391

[rebased patch onto modules-next]