handle ext3 directory corruption better (CVE-2006-6053)

I've been using Steve Grubb's purely evil "fsfuzzer" tool, at
http://people.redhat.com/sgrubb/files/fsfuzzer-0.4.tar.gz

Basically it makes a filesystem, splats some random bits over it, then
tries to mount it and do some simple filesystem actions.

At best, the filesystem catches the corruption gracefully.  At worst,
things spin out of control.

As you might guess, we found a couple places in ext3 where things spin out
of control :)

First, we had a corrupted directory that was never checked for
consistency...  it was corrupt, and pointed to another bad "entry" of
length 0.  The for() loop looped forever, since the length of
ext3_next_entry(de) was 0, and we kept looking at the same pointer over and
over and over and over...  I modeled this check and subsequent action on
what is done for other directory types in ext3_readdir...

(adding this check adds some computational expense; I am testing a followup
patch to reduce the number of times we check and re-check these directory
entries, in all cases.  Thanks for the idea, Andreas).

Next we had a root directory inode which had a corrupted size, claimed to
be > 200M on a 4M filesystem.  There was only really 1 block in the
directory, but because the size was so large, readdir kept coming back for
more, spewing thousands of printk's along the way.

Per Andreas' suggestion, if we're in this read error condition and we're
trying to read an offset which is greater than i_blocks worth of bytes,
stop trying, and break out of the loop.

With these two changes fsfuzz test survives quite well on ext3.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

diff --git a/fs/ext3/dir.c b/fs/ext3/dir.c
index 832867aef3dca61d8d2376e9ca7e14a24dbafd69..6611801322ce8e231272a3a18720422ae6f227aa 100644 (file)
--- a/fs/ext3/dir.c
+++ b/fs/ext3/dir.c
@@ -134,6 +134,9 @@ static int ext3_readdir(struct file * filp,
                        ext3_error (sb, "ext3_readdir",
                                "directory #%lu contains a hole at offset %lu",
                                inode->i_ino, (unsigned long)filp->f_pos);
+                       /* corrupt size?  Maybe no more blocks to read */
+                       if (filp->f_pos > inode->i_blocks << 9)
+                               break;
                        filp->f_pos += sb->s_blocksize - offset;
                        continue;
                }

diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
index 7be89fe95d7b4de963e87a8fc18cc2889b7980ff..3035dd4b6407240cbbad69abe3deb310b88f20ec 100644 (file)
--- a/fs/ext3/namei.c
+++ b/fs/ext3/namei.c
@@ -551,6 +551,15 @@ static int htree_dirblock_to_tree(struct file *dir_file,
                                           dir->i_sb->s_blocksize -
                                           EXT3_DIR_REC_LEN(0));
        for (; de < top; de = ext3_next_entry(de)) {
+               if (!ext3_check_dir_entry("htree_dirblock_to_tree", dir, de, bh,
+                                       (block<<EXT3_BLOCK_SIZE_BITS(dir->i_sb))
+                                               +((char *)de - bh->b_data))) {
+                       /* On error, skip the f_pos to the next block. */
+                       dir_file->f_pos = (dir_file->f_pos |
+                                       (dir->i_sb->s_blocksize - 1)) + 1;
+                       brelse (bh);
+                       return count;
+               }
                ext3fs_dirhash(de->name, de->name_len, hinfo);
                if ((hinfo->hash < start_hash) ||
                    ((hinfo->hash == start_hash) &&