ext4: Add sanity check to make_indexed_dir

Make sure the rec_len field in the '..' entry is sane, lest we overrun
the directory block and cause a kernel oops on a purposefully
corrupted filesystem.

Thanks to Sami Liedes for reporting this bug.

http://bugzilla.kernel.org/show_bug.cgi?id=12430

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

1 files changed, 15 insertions, 6 deletions

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index fec0b4c2f5f..ba702bd7910 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1368,7 +1368,7 @@ static int make_indexed_dir(handle_t *handle, struct dentry *dentry,
         struct fake_dirent *fde;
 
         blocksize =  dir->i_sb->s_blocksize;
-        dxtrace(printk(KERN_DEBUG "Creating index\n"));
+        dxtrace(printk(KERN_DEBUG "Creating index: inode %lu\n", dir->i_ino));
         retval = ext4_journal_get_write_access(handle, bh);
         if (retval) {
                 ext4_std_error(dir->i_sb, retval);
@@ -1377,6 +1377,20 @@ static int make_indexed_dir(handle_t *handle, struct dentry *dentry,
         }
         root = (struct dx_root *) bh->b_data;
 
+        /* The 0th block becomes the root, move the dirents out */
+        fde = &root->dotdot;
+        de = (struct ext4_dir_entry_2 *)((char *)fde +
+                ext4_rec_len_from_disk(fde->rec_len));
+        if ((char *) de >= (((char *) root) + blocksize)) {
+                ext4_error(dir->i_sb, __func__,
+                           "invalid rec_len for '..' in inode %lu",
+                           dir->i_ino);
+                brelse(bh);
+                return -EIO;
+        }
+        len = ((char *) root) + blocksize - (char *) de;
+
+        /* Allocate new block for the 0th block's dirents */
         bh2 = ext4_append(handle, dir, &block, &retval);
         if (!(bh2)) {
                 brelse(bh);
@@ -1385,11 +1399,6 @@ static int make_indexed_dir(handle_t *handle, struct dentry *dentry,
         EXT4_I(dir)->i_flags |= EXT4_INDEX_FL;
         data1 = bh2->b_data;
 
-        /* The 0th block becomes the root, move the dirents out */
-        fde = &root->dotdot;
-        de = (struct ext4_dir_entry_2 *)((char *)fde +
-                ext4_rec_len_from_disk(fde->rec_len));
-        len = ((char *) root) + blocksize - (char *) de;
         memcpy (data1, de, len);
         de = (struct ext4_dir_entry_2 *) data1;
         top = data1 + len;