ext4: Avoid crashing on NULL ptr dereference on a filesystem error

If the EOFBLOCK_FL flag is set when it should not be and the inode is
zero length, then eh_entries is zero, and ex is NULL, so dereferencing
ex to print ex->ee_block causes a kernel OOPS in
ext4_ext_map_blocks().

On top of that, the error message which is printed isn't very helpful.
So we fix this by printing something more explanatory which doesn't
involve trying to print ex->ee_block.

Addresses-Google-Bug: #2655740

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 5 insertions, 4 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 42d8ce91adbd..e40d2b793f2d 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3370,8 +3370,9 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
          */
         if (unlikely(path[depth].p_ext == NULL && depth != 0)) {
                 EXT4_ERROR_INODE(inode, "bad extent address "
-                                 "iblock: %d, depth: %d pblock %lld",
-                                 map->m_lblk, depth, path[depth].p_block);
+                                 "lblock: %lu, depth: %d pblock %lld",
+                                 (unsigned long) map->m_lblk, depth,
+                                 path[depth].p_block);
                 err = -EIO;
                 goto out2;
         }
@@ -3501,8 +3502,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
         if (unlikely(ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS))) {
                 if (unlikely(!eh->eh_entries)) {
                         EXT4_ERROR_INODE(inode,
-                                         "eh->eh_entries == 0 ee_block %d",
-                                         ex->ee_block);
+                                         "eh->eh_entries == 0 and "
+                                         "EOFBLOCKS_FL set");
                         err = -EIO;
                         goto out2;
                 }