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>

1 files changed, 17 insertions, 0 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 38be06354b88..64b400356cad 100644
--- 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 */