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

commit f70f362b4a6fe47c239dbfb3efc0cc2c10e4f09c upstream (as of v2.6.34-git13)

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ee9e2abb047c6b674a2d4ca89508d23834f7e404..d985da0215c7e6f94bc4382f3e1a0630e191cd4b 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3281,8 +3281,8 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
         */
        if (path[depth].p_ext == NULL && depth != 0) {
                ext4_error(inode->i_sb, __func__, "bad extent address "
-                          "inode: %lu, iblock: %d, depth: %d",
-                          inode->i_ino, iblock, depth);
+                          "inode: %lu, iblock: %lu, depth: %d",
+                          inode->i_ino, (unsigned long) iblock, depth);
                err = -EIO;
                goto out2;
        }
@@ -3418,8 +3418,11 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                } else {
                        WARN_ON(eh->eh_entries == 0);
                        ext4_error(inode->i_sb, __func__,
-                               "inode#%lu, eh->eh_entries = 0!", inode->i_ino);
-                       }
+                                  "inode#%lu, eh->eh_entries = 0 and "
+                                  "EOFBLOCKS_FL set", inode->i_ino);
+                       err = -EIO;
+                       goto out2;
+               }
        }
        err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
        if (err) {