Re: [PATCH 2/2] ext4: fix null pointer bug in move_extent.c

[Akira Fujita <a-fujita@rs.jp.nec.com>]

Hi Peng,

Peng Tao wrote:
> Will there be situations where empty extents exist in the middle of an
> extent tree? Because your patch only checks NULL extents once at the
> begining. If some NULL extents are later found in the loop, the bug
> still can be triggered and we should check NULL extents in
> mext_replace_branches().

In the case of eh->entries is 0 in ext4_ext_find_extent(),
the extent which ext4_ext_path indicates is null.
This is happened if file blocks are not allocated yet.
But an extent tree does not have empty extents in the middle of it, I think.

I have no idea we should handle empty extents case in EXT4_IOC_MOVE_EXTENTS,
but if yes, we should do null check at other places
not only mext_replace_branches().

So I add this null check to get_ext_path macro
which is used to get ext4_ext_path.

Regards,
Akira Fujita

Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
---
 move_extent.c |   32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)
--- linux-2.6.31-rc4-a/fs/ext4/move_extent.c	2009-07-23 11:32:59.000000000 +0900
+++ linux-2.6.31-rc4-b/fs/ext4/move_extent.c	2009-08-04 15:51:04.000000000 +0900
@@ -25,6 +25,8 @@
 		if (IS_ERR(path)) {					\
 			ret = PTR_ERR(path);				\
 			path = NULL;					\
+		} else if (path[ext_depth(inode)].p_ext == NULL) {	\
+			ret = -ENOENT;					\
 		}							\
 	} while (0)

@@ -284,7 +286,7 @@ mext_insert_across_blocks(handle_t *hand

 	if (new_flag) {
 		get_ext_path(orig_path, orig_inode, eblock, err);
-		if (orig_path == NULL)
+		if (err)
 			goto out;

 		if (ext4_ext_insert_extent(handle, orig_inode,
@@ -295,7 +297,7 @@ mext_insert_across_blocks(handle_t *hand
 	if (end_flag) {
 		get_ext_path(orig_path, orig_inode,
 				      le32_to_cpu(end_ext->ee_block) - 1, err);
-		if (orig_path == NULL)
+		if (err)
 			goto out;

 		if (ext4_ext_insert_extent(handle, orig_inode,
@@ -632,12 +634,12 @@ mext_replace_branches(handle_t *handle,

 	/* Get the original extent for the block "orig_off" */
 	get_ext_path(orig_path, orig_inode, orig_off, err);
-	if (orig_path == NULL)
+	if (err)
 		goto out;

 	/* Get the donor extent for the head */
 	get_ext_path(donor_path, donor_inode, donor_off, err);
-	if (donor_path == NULL)
+	if (err)
 		goto out;
 	depth = ext_depth(orig_inode);
 	oext = orig_path[depth].p_ext;
@@ -679,7 +681,7 @@ mext_replace_branches(handle_t *handle,
 		if (orig_path)
 			ext4_ext_drop_refs(orig_path);
 		get_ext_path(orig_path, orig_inode, orig_off, err);
-		if (orig_path == NULL)
+		if (err)
 			goto out;
 		depth = ext_depth(orig_inode);
 		oext = orig_path[depth].p_ext;
@@ -694,7 +696,7 @@ mext_replace_branches(handle_t *handle,
 			ext4_ext_drop_refs(donor_path);
 		get_ext_path(donor_path, donor_inode,
 				      donor_off, err);
-		if (donor_path == NULL)
+		if (err)
 			goto out;
 		depth = ext_depth(donor_inode);
 		dext = donor_path[depth].p_ext;
@@ -1138,7 +1140,7 @@ ext4_move_extents(struct file *o_filp, s
 					donor_start, &len, *moved_len);
 	mext_double_up_read(orig_inode, donor_inode);
 	if (ret)
-		goto out2;
+		goto out;

 	file_end = (i_size_read(orig_inode) - 1) >> orig_inode->i_blkbits;
 	block_end = block_start + len - 1;
@@ -1146,20 +1148,16 @@ ext4_move_extents(struct file *o_filp, s
 		len -= block_end - file_end;

 	get_ext_path(orig_path, orig_inode, block_start, ret);
-	if (orig_path == NULL)
-		goto out2;
+	if (ret)
+		goto out;

 	/* Get path structure to check the hole */
 	get_ext_path(holecheck_path, orig_inode, block_start, ret);
-	if (holecheck_path == NULL)
+	if (ret)
 		goto out;

 	depth = ext_depth(orig_inode);
 	ext_cur = holecheck_path[depth].p_ext;
-	if (ext_cur == NULL) {
-		ret = -EINVAL;
-		goto out;
-	}

 	/*
 	 * Get proper extent whose ee_block is beyond block_start
@@ -1282,7 +1280,7 @@ ext4_move_extents(struct file *o_filp, s
 			ext4_ext_drop_refs(holecheck_path);
 		get_ext_path(holecheck_path, orig_inode,
 				      seq_start, ret);
-		if (holecheck_path == NULL)
+		if (ret)
 			break;
 		depth = holecheck_path->p_depth;

@@ -1290,7 +1288,7 @@ ext4_move_extents(struct file *o_filp, s
 		if (orig_path)
 			ext4_ext_drop_refs(orig_path);
 		get_ext_path(orig_path, orig_inode, seq_start, ret);
-		if (orig_path == NULL)
+		if (ret)
 			break;

 		ext_cur = holecheck_path[depth].p_ext;
@@ -1307,7 +1305,7 @@ out:
 		ext4_ext_drop_refs(holecheck_path);
 		kfree(holecheck_path);
 	}
-out2:
+
 	mext_inode_double_unlock(orig_inode, donor_inode);

 	if (ret)