1 files changed, 42 insertions, 6 deletions

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index f2f482bec573..a6e74514e662 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -1123,6 +1123,33 @@ static unsigned long mtdchar_get_unmapped_area(struct file *file,
 }
 #endif
 
+static inline unsigned long get_vm_size(struct vm_area_struct *vma)
+{
+        return vma->vm_end - vma->vm_start;
+}
+
+static inline resource_size_t get_vm_offset(struct vm_area_struct *vma)
+{
+        return (resource_size_t) vma->vm_pgoff << PAGE_SHIFT;
+}
+
+/*
+ * Set a new vm offset.
+ *
+ * Verify that the incoming offset really works as a page offset,
+ * and that the offset and size fit in a resource_size_t.
+ */
+static inline int set_vm_offset(struct vm_area_struct *vma, resource_size_t off)
+{
+        pgoff_t pgoff = off >> PAGE_SHIFT;
+        if (off != (resource_size_t) pgoff << PAGE_SHIFT)
+                return -EINVAL;
+        if (off + get_vm_size(vma) - 1 < off)
+                return -EINVAL;
+        vma->vm_pgoff = pgoff;
+        return 0;
+}
+
 /*
  * set up a mapping for shared memory segments
  */
@@ -1132,20 +1159,29 @@ static int mtdchar_mmap(struct file *file, struct vm_area_struct *vma)
         struct mtd_file_info *mfi = file->private_data;
         struct mtd_info *mtd = mfi->mtd;
         struct map_info *map = mtd->priv;
-        unsigned long start;
-        unsigned long off;
-        u32 len;
+        resource_size_t start, off;
+        unsigned long len, vma_len;
 
         if (mtd->type == MTD_RAM || mtd->type == MTD_ROM) {
-                off = vma->vm_pgoff << PAGE_SHIFT;
+                off = get_vm_offset(vma);
                 start = map->phys;
                 len = PAGE_ALIGN((start & ~PAGE_MASK) + map->size);
                 start &= PAGE_MASK;
-                if ((vma->vm_end - vma->vm_start + off) > len)
+                vma_len = get_vm_size(vma);
+
+                /* Overflow in off+len? */
+                if (vma_len + off < off)
+                        return -EINVAL;
+                /* Does it fit in the mapping? */
+                if (vma_len + off > len)
                         return -EINVAL;
 
                 off += start;
-                vma->vm_pgoff = off >> PAGE_SHIFT;
+                /* Did that overflow? */
+                if (off < start)
+                        return -EINVAL;
+                if (set_vm_offset(vma, off) < 0)
+                        return -EINVAL;
                 vma->vm_flags |= VM_IO | VM_RESERVED;
 
 #ifdef pgprot_noncached