ext4: always check ext4_ext_find_extent result

Where are some places where logic guaranties us that extent we are
searching exits, but this may not be true due to on-disk data
corruption. If such corruption happens we must prevent possible
null pointer dereferences.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 38be063..64b4003 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3313,6 +3313,11 @@ static int ext4_split_extent(handle_t *handle,
                return PTR_ERR(path);
        depth = ext_depth(inode);
        ex = path[depth].p_ext;
+       if (!ex) {
+               EXT4_ERROR_INODE(inode, "unexpected hole at %lu",
+                                (unsigned long) map->m_lblk);
+               return -EIO;
+       }
        uninitialized = ext4_ext_is_uninitialized(ex);
        split_flag1 = 0;
 
@@ -3694,6 +3699,12 @@ static int ext4_convert_initialized_extents(handle_t *handle,
                }
                depth = ext_depth(inode);
                ex = path[depth].p_ext;
+               if (!ex) {
+                       EXT4_ERROR_INODE(inode, "unexpected hole at %lu",
+                                        (unsigned long) map->m_lblk);
+                       err = -EIO;
+                       goto out;
+               }
        }
 
        err = ext4_ext_get_access(handle, inode, path + depth);
@@ -5340,6 +5351,12 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
                        return PTR_ERR(path);
                depth = path->p_depth;
                extent = path[depth].p_ext;
+               if (!extent) {
+                       EXT4_ERROR_INODE(inode, "unexpected hole at %lu",
+                                        (unsigned long) start);
+                       return -EIO;
+               }
+
                current_block = le32_to_cpu(extent->ee_block);
                if (start > current_block) {
                        /* Hole, move to the next extent */