[PATCH] NOMMU: Check that access_process_vm() has a valid target

Check that access_process_vm() is accessing a valid mapping in the target
process.

This limits ptrace() accesses and accesses through /proc/<pid>/maps to only
those regions actually mapped by a program.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 100 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index f2ef1dcfff7..601159a46ab 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2604,3 +2604,56 @@ int in_gate_area_no_task(unsigned long addr)
 }
 
 #endif	/* __HAVE_ARCH_GATE_AREA */
+
+/*
+ * Access another process' address space.
+ * Source/target buffer must be kernel space,
+ * Do not walk the page table directly, use get_user_pages
+ */
+int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
+{
+	struct mm_struct *mm;
+	struct vm_area_struct *vma;
+	struct page *page;
+	void *old_buf = buf;
+
+	mm = get_task_mm(tsk);
+	if (!mm)
+		return 0;
+
+	down_read(&mm->mmap_sem);
+	/* ignore errors, just check how much was sucessfully transfered */
+	while (len) {
+		int bytes, ret, offset;
+		void *maddr;
+
+		ret = get_user_pages(tsk, mm, addr, 1,
+				write, 1, &page, &vma);
+		if (ret <= 0)
+			break;
+
+		bytes = len;
+		offset = addr & (PAGE_SIZE-1);
+		if (bytes > PAGE_SIZE-offset)
+			bytes = PAGE_SIZE-offset;
+
+		maddr = kmap(page);
+		if (write) {
+			copy_to_user_page(vma, page, addr,
+					  maddr + offset, buf, bytes);
+			set_page_dirty_lock(page);
+		} else {
+			copy_from_user_page(vma, page, addr,
+					    buf, maddr + offset, bytes);
+		}
+		kunmap(page);
+		page_cache_release(page);
+		len -= bytes;
+		buf += bytes;
+		addr += bytes;
+	}
+	up_read(&mm->mmap_sem);
+	mmput(mm);
+
+	return buf - old_buf;
+}
diff --git a/mm/nommu.c b/mm/nommu.c
index d99dea31e44..d08acdae003 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1206,3 +1206,50 @@ struct page *filemap_nopage(struct vm_area_struct *area,
 	BUG();
 	return NULL;
 }
+
+/*
+ * Access another process' address space.
+ * - source/target buffer must be kernel space
+ */
+int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
+{
+	struct vm_list_struct *vml;
+	struct vm_area_struct *vma;
+	struct mm_struct *mm;
+
+	if (addr + len < addr)
+		return 0;
+
+	mm = get_task_mm(tsk);
+	if (!mm)
+		return 0;
+
+	down_read(&mm->mmap_sem);
+
+	/* the access must start within one of the target process's mappings */
+	for (vml = mm->context.vmlist; vml; vml = vml->next)
+		if (addr >= vml->vma->vm_start && addr < vml->vma->vm_end)
+			break;
+
+	if (vml) {
+		vma = vml->vma;
+
+		/* don't overrun this mapping */
+		if (addr + len >= vma->vm_end)
+			len = vma->vm_end - addr;
+
+		/* only read or write mappings where it is permitted */
+		if (write && vma->vm_flags & VM_WRITE)
+			len -= copy_to_user((void *) addr, buf, len);
+		else if (!write && vma->vm_flags & VM_READ)
+			len -= copy_from_user(buf, (void *) addr, len);
+		else
+			len = 0;
+	} else {
+		len = 0;
+	}
+
+	up_read(&mm->mmap_sem);
+	mmput(mm);
+	return len;
+}