From eaca4fd8265aa05c5b07aaa425e058abd0aa38d5 Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Sat, 30 Dec 2006 18:22:07 -0500 Subject: [PATCH] [PATCH] 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 Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Chris Wright --- fs/ext3/dir.c | 3 +++ fs/ext3/namei.c | 9 +++++++++ 2 files changed, 12 insertions(+) diff --git a/fs/ext3/dir.c b/fs/ext3/dir.c index d0b54f30b914..5a9313ecd4ef 100644 --- a/fs/ext3/dir.c +++ b/fs/ext3/dir.c @@ -154,6 +154,9 @@ 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 906731a20f1a..60d2f9dbdb00 100644 --- a/fs/ext3/namei.c +++ b/fs/ext3/namei.c @@ -552,6 +552,15 @@ 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<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) && -- 2.39.5