coredump: fix spam with zero VMA process

Nobody ever tried to self destruct by unmapping whole address space at
once:

munmap((void *)0, (1ULL << 47) - 4096);

Doing this produces 2 warnings for zero-length vmalloc allocations:

a.out[1353]: segfault at 7f80bcc4b757 ip 00007f80bcc4b757 sp 00007fff683939b8 error 14
a.out: vmalloc: allocation failure: 0 bytes, mode:0xcc0(GFP_KERNEL), nodemask=(null)
...
a.out: vmalloc: allocation failure: 0 bytes, mode:0xcc0(GFP_KERNEL), nodemask=(null)
...

Fix is to switch to kvmalloc().

Steps to reproduce:

// vsyscall=none
#include <sys/mman.h>
#include <sys/resource.h>
int main(void)
{
setrlimit(RLIMIT_CORE, &(struct rlimit){RLIM_INFINITY, RLIM_INFINITY});
munmap((void *)0, (1ULL << 47) - 4096);
return 0;
}

Link: http://lkml.kernel.org/r/20180410180353.GA2515@avx2
Signed-off-by: Alexey Dobriyan <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/binfmt_elf.c

···
 	if (size >= MAX_FILE_NOTE_SIZE) /* paranoia check */
 		return -EINVAL;
 	size = round_up(size, PAGE_SIZE);
-	data = vmalloc(size);
-	if (!data)
+	data = kvmalloc(size, GFP_KERNEL);
+	if (ZERO_OR_NULL_PTR(data))
 		return -ENOMEM;
 
 	start_end_ofs = data + 2;
···
 		filename = file_path(file, name_curpos, remaining);
 		if (IS_ERR(filename)) {
 			if (PTR_ERR(filename) == -ENAMETOOLONG) {
-				vfree(data);
+				kvfree(data);
 				size = size * 5 / 4;
 				goto alloc;
 			}
···
 		kfree(t);
 	}
 	kfree(info->psinfo.data);
-	vfree(info->files.data);
+	kvfree(info->files.data);
 }
 
 #else
···
 
 	/* Free data possibly allocated by fill_files_note(): */
 	if (info->notes_files)
-		vfree(info->notes_files->data);
+		kvfree(info->notes_files->data);
 
 	kfree(info->prstatus);
 	kfree(info->psinfo);
···
 
 	if (segs - 1 > ULONG_MAX / sizeof(*vma_filesz))
 		goto end_coredump;
-	vma_filesz = vmalloc(array_size(sizeof(*vma_filesz), (segs - 1)));
-	if (!vma_filesz)
+	vma_filesz = kvmalloc(array_size(sizeof(*vma_filesz), (segs - 1)),
+			      GFP_KERNEL);
+	if (ZERO_OR_NULL_PTR(vma_filesz))
 		goto end_coredump;
 
 	for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
···
 cleanup:
 	free_note_info(&info);
 	kfree(shdr4extnum);
-	vfree(vma_filesz);
+	kvfree(vma_filesz);
 	kfree(phdr4note);
 	kfree(elf);
 out: