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

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index fec0b4c2f5f1904c89436c1f825e82338489232f..ba702bd7910d955629d7ae049d1fb6930681d893 100644 (file)
--- 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;