A maliciously corrupted filesystem can contain cycles in the h-tree stored inside a directory. That can easily lead to the kernel corrupting tree nodes that were already verified under its hands while doing a node split and consequently accessing unallocated memory. Fix the problem by verifying traversed block numbers are unique.
CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz --- fs/ext4/namei.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index ca6ee9940599..06441ad6104d 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -777,12 +777,14 @@ static struct dx_frame * dx_probe(struct ext4_filename *fname, struct inode *dir, struct dx_hash_info *hinfo, struct dx_frame *frame_in) { - unsigned count, indirect; + unsigned count, indirect, level, i; struct dx_entry *at, *entries, *p, *q, *m; struct dx_root *root; struct dx_frame *frame = frame_in; struct dx_frame *ret_err = ERR_PTR(ERR_BAD_DX_DIR); u32 hash; + ext4_lblk_t block; + ext4_lblk_t blocks[EXT4_HTREE_LEVEL];
memset(frame_in, 0, EXT4_HTREE_LEVEL * sizeof(frame_in[0])); frame->bh = ext4_read_dirblock(dir, 0, INDEX); @@ -854,6 +856,8 @@ dx_probe(struct ext4_filename *fname, struct inode *dir, }
dxtrace(printk("Look up %x", hash)); + level = 0; + blocks[0] = 0; while (1) { count = dx_get_count(entries); if (!count || count > dx_get_limit(entries)) { @@ -882,15 +886,27 @@ dx_probe(struct ext4_filename *fname, struct inode *dir, dx_get_block(at))); frame->entries = entries; frame->at = at; - if (!indirect--) + + block = dx_get_block(at); + for (i = 0; i <= level; i++) { + if (blocks[i] == block) { + ext4_warning_inode(dir, + "dx entry: tree cycle block %u points back to block %u", + blocks[level], block); + goto fail; + } + } + blocks[++level] = block; + if (level > indirect) return frame; frame++; - frame->bh = ext4_read_dirblock(dir, dx_get_block(at), INDEX); + frame->bh = ext4_read_dirblock(dir, block, INDEX); if (IS_ERR(frame->bh)) { ret_err = (struct dx_frame *) frame->bh; frame->bh = NULL; goto fail; } + entries = ((struct dx_node *) frame->bh->b_data)->entries;
if (dx_get_limit(entries) != dx_node_limit(dir)) { @@ -1278,7 +1294,7 @@ static int dx_make_map(struct inode *dir, struct buffer_head *bh, count++; cond_resched(); } - de = ext4_next_entry(de, blocksize); + de = ext4_next_entry(de, dir->i_sb->s_blocksize); } return count; }