CVE-2011-3638 (C, published 2013-03-01T12:37Z)
Description: value: fs/ext4/extents.c in the Linux kernel before 3.0 does not mark a modified extent as dirty in certain cases of extent splitting, which allows local users to cause a denial of service (system crash) via vectors involving ext4 umount and mount operations.
Severity: MEDIUM (CVSS v3 base score: )
Weakness: NVD-CWE-noinfo \u2014 Insufficient Information
There is insufficient information about the issue to classify it; details are unkown or unspecified.
Repository: https://github.com/torvalds/linux
Files changed:
fs/ext4/extents.c
Commit message: ext4: reimplement convert and split_unwritten

Reimplement ext4_ext_convert_to_initialized() and
ext4_split_unwritten_extents() using ext4_split_extent()

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Tested-by: Allison Henderson <achender@linux.vnet.ibm.com>


Vulnerable code:
	struct ext4_extent *ex, newex, orig_ex;
	struct ext4_extent *ex1 = NULL;
	struct ext4_extent *ex2 = NULL;
	struct ext4_extent *ex3 = NULL;
	struct ext4_extent_header *eh;
	ext4_fsblk_t newblock;
	int ret = 0;
	int may_zeroout;
	eh = path[depth].p_hdr;
	newblock = map->m_lblk - ee_block + ext4_ext_pblock(ex);

	ex2 = ex;
	orig_ex.ee_block = ex->ee_block;
	orig_ex.ee_len   = cpu_to_le16(ee_len);
	ext4_ext_store_pblock(&orig_ex, ext4_ext_pblock(ex));
	may_zeroout = ee_block + ee_len <= eof_block;
	err = ext4_ext_get_access(handle, inode, path + depth);
	if (err)
		goto out;
	if (ee_len <= 2*EXT4_EXT_ZERO_LEN && may_zeroout) {
		err =  ext4_ext_zeroout(inode, &orig_ex);
			goto fix_extent_len;
		/* update the extent length and mark as initialized */
		ex->ee_block = orig_ex.ee_block;
		ex->ee_len   = orig_ex.ee_len;
		ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
		ext4_ext_dirty(handle, inode, path + depth);
		/* zeroed the full extent */
		return allocated;
	}

	/* ex1: ee_block to map->m_lblk - 1 : uninitialized */
	if (map->m_lblk > ee_block) {
		ex1 = ex;
		ex1->ee_len = cpu_to_le16(map->m_lblk - ee_block);
		ext4_ext_mark_uninitialized(ex1);
		ex2 = &newex;
	}
	/*
	 * for sanity, update the length of the ex2 extent before
	 * we insert ex3, if ex1 is NULL. This is to avoid temporary
	 * overlap of blocks.
	 */
	if (!ex1 && allocated > map->m_len)
		ex2->ee_len = cpu_to_le16(map->m_len);
	/* ex3: to ee_block + ee_len : uninitialised */
	if (allocated > map->m_len) {
		unsigned int newdepth;
		/* If extent has less than EXT4_EXT_ZERO_LEN zerout directly */
		if (allocated <= EXT4_EXT_ZERO_LEN && may_zeroout) {
			/*
			 * map->m_lblk == ee_block is handled by the zerouout
			 * at the beginning.
			 * Mark first half uninitialized.
			 * Mark second half initialized and zero out the
			 * initialized extent
			 */
			ex->ee_block = orig_ex.ee_block;
			ex->ee_len   = cpu_to_le16(ee_len - allocated);
			ext4_ext_mark_uninitialized(ex);
			ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
			ext4_ext_dirty(handle, inode, path + depth);

			ex3 = &newex;
			ex3->ee_block = cpu_to_le32(map->m_lblk);
			ext4_ext_store_pblock(ex3, newblock);
			ex3->ee_len = cpu_to_le16(allocated);
			err = ext4_ext_insert_extent(handle, inode, path,
							ex3, 0);
			if (err == -ENOSPC) {
				err =  ext4_ext_zeroout(inode, &orig_ex);
				if (err)
					goto fix_extent_len;
				ex->ee_block = orig_ex.ee_block;
				ex->ee_len   = orig_ex.ee_len;
				ext4_ext_store_pblock(ex,
					ext4_ext_pblock(&orig_ex));
				ext4_ext_dirty(handle, inode, path + depth);
				/* blocks available from map->m_lblk */
				return allocated;

			} else if (err)
				goto fix_extent_len;

			/*
			 * We need to zero out the second half because
			 * an fallocate request can update file size and
			 * converting the second half to initialized extent
			 * implies that we can leak some junk data to user
			 * space.
			 */
			err =  ext4_ext_zeroout(inode, ex3);
			if (err) {
				/*
				 * We should actually mark the
				 * second half as uninit and return error
				 * Insert would have changed the extent
				 */
				depth = ext_depth(inode);
				ext4_ext_drop_refs(path);
				path = ext4_ext_find_extent(inode, map->m_lblk,
							    path);
				if (IS_ERR(path)) {
					err = PTR_ERR(path);
					return err;
				}
				/* get the second half extent details */
				ex = path[depth].p_ext;
				err = ext4_ext_get_access(handle, inode,
								path + depth);
				if (err)
					return err;
				ext4_ext_mark_uninitialized(ex);
				ext4_ext_dirty(handle, inode, path + depth);
				return err;
			}

			/* zeroed the second half */
			return allocated;
		}
		ex3 = &newex;
		ex3->ee_block = cpu_to_le32(map->m_lblk + map->m_len);
		ext4_ext_store_pblock(ex3, newblock + map->m_len);
		ex3->ee_len = cpu_to_le16(allocated - map->m_len);
		ext4_ext_mark_uninitialized(ex3);
		err = ext4_ext_insert_extent(handle, inode, path, ex3, 0);
		if (err == -ENOSPC && may_zeroout) {
			err =  ext4_ext_zeroout(inode, &orig_ex);
			if (err)
				goto fix_extent_len;
			/* update the extent length and mark as initialized */
			ex->ee_block = orig_ex.ee_block;
			ex->ee_len   = orig_ex.ee_len;
			ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
			ext4_ext_dirty(handle, inode, path + depth);
			/* zeroed the full extent */
			/* blocks available from map->m_lblk */
			return allocated;

		} else if (err)
			goto fix_extent_len;
		/*
		 * The depth, and hence eh & ex might change
		 * as part of the insert above.
		 */
		newdepth = ext_depth(inode);
		/*
		 * update the extent length after successful insert of the
		 * split extent
		 */
		ee_len -= ext4_ext_get_actual_len(ex3);
		orig_ex.ee_len = cpu_to_le16(ee_len);
		may_zeroout = ee_block + ee_len <= eof_block;

		depth = newdepth;
		ext4_ext_drop_refs(path);
		path = ext4_ext_find_extent(inode, map->m_lblk, path);
		if (IS_ERR(path)) {
			err = PTR_ERR(path);
		}
		eh = path[depth].p_hdr;
		ex = path[depth].p_ext;
		if (ex2 != &newex)
			ex2 = ex;

		allocated = map->m_len;

		/* If extent has less than EXT4_EXT_ZERO_LEN and we are trying
		 * to insert a extent in the middle zerout directly
		 * otherwise give the extent a chance to merge to left
		 */
		if (le16_to_cpu(orig_ex.ee_len) <= EXT4_EXT_ZERO_LEN &&
			map->m_lblk != ee_block && may_zeroout) {
			err =  ext4_ext_zeroout(inode, &orig_ex);
			if (err)
				goto fix_extent_len;
			/* update the extent length and mark as initialized */
			ex->ee_block = orig_ex.ee_block;
			ex->ee_len   = orig_ex.ee_len;
			ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
			ext4_ext_dirty(handle, inode, path + depth);
			/* zero out the first half */
			/* blocks available from map->m_lblk */
			return allocated;
		}
	}
	/*
	 * If there was a change of depth as part of the
	 * insertion of ex3 above, we need to update the length
	 * of the ex1 extent again here
	 */
	if (ex1 && ex1 != ex) {
		ex1 = ex;
		ex1->ee_len = cpu_to_le16(map->m_lblk - ee_block);
		ext4_ext_mark_uninitialized(ex1);
		ex2 = &newex;
	}
	/* ex2: map->m_lblk to map->m_lblk + maxblocks-1 : initialised */
	ex2->ee_block = cpu_to_le32(map->m_lblk);
	ext4_ext_store_pblock(ex2, newblock);
	ex2->ee_len = cpu_to_le16(allocated);
	if (ex2 != ex)
		goto insert;
	/*
	 * New (initialized) extent starts from the first block
	 * in the current extent. i.e., ex2 == ex
	 * We have to see if it can be merged with the extent
	 * on the left.
	 */
	if (ex2 > EXT_FIRST_EXTENT(eh)) {
		/*
		 * To merge left, pass "ex2 - 1" to try_to_merge(),
		 * since it merges towards right _only_.
		 */
		ret = ext4_ext_try_to_merge(inode, path, ex2 - 1);
		if (ret) {
			err = ext4_ext_correct_indexes(handle, inode, path);
			if (err)
				goto out;
			depth = ext_depth(inode);
			ex2--;
		}
	 * Try to Merge towards right. This might be required
	 * only when the whole extent is being written to.
	 * i.e. ex2 == ex and ex3 == NULL.
	if (!ex3) {
		ret = ext4_ext_try_to_merge(inode, path, ex2);
		if (ret) {
			err = ext4_ext_correct_indexes(handle, inode, path);
	/* Mark modified extent as dirty */
	err = ext4_ext_dirty(handle, inode, path + depth);
	goto out;
insert:
	err = ext4_ext_insert_extent(handle, inode, path, &newex, 0);
	if (err == -ENOSPC && may_zeroout) {
		err =  ext4_ext_zeroout(inode, &orig_ex);
		if (err)
			goto fix_extent_len;
		/* update the extent length and mark as initialized */
		ex->ee_block = orig_ex.ee_block;
		ex->ee_len   = orig_ex.ee_len;
		ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
		ext4_ext_dirty(handle, inode, path + depth);
		/* zero out the first half */
		return allocated;
	} else if (err)
		goto fix_extent_len;
	ext4_ext_show_leaf(inode, path);

fix_extent_len:
	ex->ee_block = orig_ex.ee_block;
	ex->ee_len   = orig_ex.ee_len;
	ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
	ext4_ext_mark_uninitialized(ex);
	ext4_ext_dirty(handle, inode, path + depth);
	return err;
	struct ext4_extent *ex, newex, orig_ex;
	struct ext4_extent *ex1 = NULL;
	struct ext4_extent *ex2 = NULL;
	struct ext4_extent *ex3 = NULL;
	ext4_lblk_t ee_block, eof_block;
	unsigned int allocated, ee_len, depth;
	ext4_fsblk_t newblock;
	int err = 0;
	int may_zeroout;

	depth = ext_depth(inode);
	ex = path[depth].p_ext;
	ee_block = le32_to_cpu(ex->ee_block);
	ee_len = ext4_ext_get_actual_len(ex);
	allocated = ee_len - (map->m_lblk - ee_block);
	newblock = map->m_lblk - ee_block + ext4_ext_pblock(ex);

	ex2 = ex;
	orig_ex.ee_block = ex->ee_block;
	orig_ex.ee_len   = cpu_to_le16(ee_len);
	ext4_ext_store_pblock(&orig_ex, ext4_ext_pblock(ex));

	may_zeroout = ee_block + ee_len <= eof_block;

	/*
 	 * If the uninitialized extent begins at the same logical
 	 * block where the write begins, and the write completely
 	 * covers the extent, then we don't need to split it.
 	 */
	if ((map->m_lblk == ee_block) && (allocated <= map->m_len))
		return allocated;

	err = ext4_ext_get_access(handle, inode, path + depth);
	if (err)
		goto out;
	/* ex1: ee_block to map->m_lblk - 1 : uninitialized */
	if (map->m_lblk > ee_block) {
		ex1 = ex;
		ex1->ee_len = cpu_to_le16(map->m_lblk - ee_block);
		ext4_ext_mark_uninitialized(ex1);
		ex2 = &newex;
	}
	/*
	 * for sanity, update the length of the ex2 extent before
	 * we insert ex3, if ex1 is NULL. This is to avoid temporary
	 * overlap of blocks.
	 */
	if (!ex1 && allocated > map->m_len)
		ex2->ee_len = cpu_to_le16(map->m_len);
	/* ex3: to ee_block + ee_len : uninitialised */
	if (allocated > map->m_len) {
		unsigned int newdepth;
		ex3 = &newex;
		ex3->ee_block = cpu_to_le32(map->m_lblk + map->m_len);
		ext4_ext_store_pblock(ex3, newblock + map->m_len);
		ex3->ee_len = cpu_to_le16(allocated - map->m_len);
		ext4_ext_mark_uninitialized(ex3);
		err = ext4_ext_insert_extent(handle, inode, path, ex3, flags);
		if (err == -ENOSPC && may_zeroout) {
			err =  ext4_ext_zeroout(inode, &orig_ex);
			if (err)
				goto fix_extent_len;
			/* update the extent length and mark as initialized */
			ex->ee_block = orig_ex.ee_block;
			ex->ee_len   = orig_ex.ee_len;
			ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
			ext4_ext_dirty(handle, inode, path + depth);
			/* zeroed the full extent */
			/* blocks available from map->m_lblk */
			return allocated;

		} else if (err)
			goto fix_extent_len;
		/*
		 * The depth, and hence eh & ex might change
		 * as part of the insert above.
		 */
		newdepth = ext_depth(inode);
		/*
		 * update the extent length after successful insert of the
		 * split extent
		 */
		ee_len -= ext4_ext_get_actual_len(ex3);
		orig_ex.ee_len = cpu_to_le16(ee_len);
		may_zeroout = ee_block + ee_len <= eof_block;

		depth = newdepth;
		ext4_ext_drop_refs(path);
		path = ext4_ext_find_extent(inode, map->m_lblk, path);
		if (IS_ERR(path)) {
			err = PTR_ERR(path);
			goto out;
		}
		ex = path[depth].p_ext;
		if (ex2 != &newex)
			ex2 = ex;
		err = ext4_ext_get_access(handle, inode, path + depth);
		if (err)
			goto out;
		allocated = map->m_len;
	}
	/*
	 * If there was a change of depth as part of the
	 * insertion of ex3 above, we need to update the length
	 * of the ex1 extent again here
	 */
	if (ex1 && ex1 != ex) {
		ex1 = ex;
		ex1->ee_len = cpu_to_le16(map->m_lblk - ee_block);
		ext4_ext_mark_uninitialized(ex1);
		ex2 = &newex;
	}
	/*
	 * ex2: map->m_lblk to map->m_lblk + map->m_len-1 : to be written
	 * using direct I/O, uninitialised still.
	 */
	ex2->ee_block = cpu_to_le32(map->m_lblk);
	ext4_ext_store_pblock(ex2, newblock);
	ex2->ee_len = cpu_to_le16(allocated);
	ext4_ext_mark_uninitialized(ex2);
	if (ex2 != ex)
		goto insert;
	/* Mark modified extent as dirty */
	err = ext4_ext_dirty(handle, inode, path + depth);
	ext_debug("out here\n");
	goto out;
insert:
	err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
	if (err == -ENOSPC && may_zeroout) {
		err =  ext4_ext_zeroout(inode, &orig_ex);
		if (err)
			goto fix_extent_len;
		/* update the extent length and mark as initialized */
		ex->ee_block = orig_ex.ee_block;
		ex->ee_len   = orig_ex.ee_len;
		ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
		ext4_ext_dirty(handle, inode, path + depth);
		/* zero out the first half */
		return allocated;
	} else if (err)
		goto fix_extent_len;
out:
	ext4_ext_show_leaf(inode, path);
	return err ? err : allocated;

fix_extent_len:
	ex->ee_block = orig_ex.ee_block;
	ex->ee_len   = orig_ex.ee_len;
	ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
	ext4_ext_mark_uninitialized(ex);
	ext4_ext_dirty(handle, inode, path + depth);
	return err;

Fixed code:
	struct ext4_map_blocks split_map;
	struct ext4_extent zero_ex;
	struct ext4_extent *ex;
	int split_flag = 0;
	WARN_ON(map->m_lblk < ee_block);
	split_flag |= ee_block + ee_len <= eof_block ? EXT4_EXT_MAY_ZEROOUT : 0;
	if (ee_len <= 2*EXT4_EXT_ZERO_LEN &&
	    (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
		err = ext4_ext_zeroout(inode, ex);
		ext4_ext_mark_initialized(ex);
		ext4_ext_try_to_merge(inode, path, ex);
		err = ext4_ext_dirty(handle, inode, path + depth);
		goto out;

	 * four cases:
	 * 1. split the extent into three extents.
	 * 2. split the extent into two extents, zeroout the first half.
	 * 3. split the extent into two extents, zeroout the second half.
	 * 4. split the extent into two extents with out zeroout.
	split_map.m_lblk = map->m_lblk;
	split_map.m_len = map->m_len;

	if (allocated > map->m_len) {
		if (allocated <= EXT4_EXT_ZERO_LEN &&
		    (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
			/* case 3 */
			zero_ex.ee_block =
					 cpu_to_le32(map->m_lblk + map->m_len);
			zero_ex.ee_len = cpu_to_le16(allocated - map->m_len);
			ext4_ext_store_pblock(&zero_ex,
				ext4_ext_pblock(ex) + map->m_lblk - ee_block);
			err = ext4_ext_zeroout(inode, &zero_ex);
			split_map.m_lblk = map->m_lblk;
			split_map.m_len = allocated;
		} else if ((map->m_lblk - ee_block + map->m_len <
			   EXT4_EXT_ZERO_LEN) &&
			   (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
			/* case 2 */
			if (map->m_lblk != ee_block) {
				zero_ex.ee_block = ex->ee_block;
				zero_ex.ee_len = cpu_to_le16(map->m_lblk -
							ee_block);
				ext4_ext_store_pblock(&zero_ex,
						      ext4_ext_pblock(ex));
				err = ext4_ext_zeroout(inode, &zero_ex);
				if (err)
					goto out;
			}

			allocated = map->m_lblk - ee_block + map->m_len;

			split_map.m_lblk = ee_block;
			split_map.m_len = allocated;

	allocated = ext4_split_extent(handle, inode, path,
				       &split_map, split_flag, 0);
	if (allocated < 0)
		err = allocated;

	ext4_lblk_t eof_block;
	ext4_lblk_t ee_block;
	struct ext4_extent *ex;
	unsigned int ee_len;
	int split_flag = 0, depth;
	depth = ext_depth(inode);
	ex = path[depth].p_ext;
	ee_block = le32_to_cpu(ex->ee_block);
	ee_len = ext4_ext_get_actual_len(ex);
	split_flag |= ee_block + ee_len <= eof_block ? EXT4_EXT_MAY_ZEROOUT : 0;
	split_flag |= EXT4_EXT_MARK_UNINIT2;
	flags |= EXT4_GET_BLOCKS_PRE_IO;
	return ext4_split_extent(handle, inode, path, map, split_flag, flags);