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

commit f70f362b4a6fe47c239dbfb3efc0cc2c10e4f09c upstream.

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: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index a1d3f7c1e7ce98e728a15e206af24a160e9b3e7b..8e8a7a4eedff6fbad9d72e127affe9a3982546e1 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3381,8 +3381,9 @@ int ext4_ext_get_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",
-                                iblock, depth, path[depth].p_block);
+                                "iblock: %lu, depth: %d pblock %lld",
+                                (unsigned long) iblock, depth,
+                                path[depth].p_block);
                err = -EIO;
                goto out2;
        }
@@ -3512,8 +3513,8 @@ int ext4_ext_get_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;
                }