kcore: /proc/kcore should use vread

/proc/kcore has its own routine to access vmallc area.  It can be replaced
with vread().  And by this, /proc/kcore can do safe access to vmalloc
area.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Mike Smith <scgtrp@gmail.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/kcore.c

@@ -328,43 +328,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 				return -EFAULT;
 		} else if (is_vmalloc_addr((void *)start)) {
 			char * elf_buf;
-			struct vm_struct *m;
-			unsigned long curstart = start;
-			unsigned long cursize = tsz;
 
 			elf_buf = kzalloc(tsz, GFP_KERNEL);
 			if (!elf_buf)
 				return -ENOMEM;
-
-			read_lock(&vmlist_lock);
-			for (m=vmlist; m && cursize; m=m->next) {
-				unsigned long vmstart;
-				unsigned long vmsize;
-				unsigned long msize = m->size - PAGE_SIZE;
-
-				if (((unsigned long)m->addr + msize) < 
-								curstart)
-					continue;
-				if ((unsigned long)m->addr > (curstart + 
-								cursize))
-					break;
-				vmstart = (curstart < (unsigned long)m->addr ? 
-					(unsigned long)m->addr : curstart);
-				if (((unsigned long)m->addr + msize) > 
-							(curstart + cursize))
-					vmsize = curstart + cursize - vmstart;
-				else
-					vmsize = (unsigned long)m->addr + 
-							msize - vmstart;
-				curstart = vmstart + vmsize;
-				cursize -= vmsize;
-				/* don't dump ioremap'd stuff! (TA) */
-				if (m->flags & VM_IOREMAP)
-					continue;
-				memcpy(elf_buf + (vmstart - start),
-					(char *)vmstart, vmsize);
-			}
-			read_unlock(&vmlist_lock);
+			vread(elf_buf, (char *)start, tsz);
+			/* we have to zero-fill user buffer even if no read */
 			if (copy_to_user(buffer, elf_buf, tsz)) {
 				kfree(elf_buf);
 				return -EFAULT;