[PATCH v2 2/2] ocfs2: bound-check dir entries in the inline-data re-validation scan

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

ocfs2_dir_foreach_blk_id() re-scans the inline data area the same way
ocfs2_dir_foreach_blk_el() re-scans a directory block, and is missing the
same two bounds:

	for (i = 0; i < i_size_read(inode) && i < offset; ) {
		de = (struct ocfs2_dir_entry *)(data->id_data + i);
		if (le16_to_cpu(de->rec_len) < OCFS2_DIR_REC_LEN(1))
			break;
		i += le16_to_cpu(de->rec_len);
	}

ocfs2_validate_inode_block() keeps i_size inside the inline area:

	if (le16_to_cpu(data->id_count) >
	    ocfs2_max_inline_data_with_xattr(sb, di))
	if (le64_to_cpu(di->i_size) > le16_to_cpu(data->id_count))

and that area runs to the end of the inode block, so for a full inline
directory data->id_data + i_size is the end of di_bh->b_data.  A bogus
rec_len leaves i in the last OCFS2_DIR_REC_LEN(1) - 1 bytes of it, and
de->rec_len, at byte offset 8 within the entry, is then read past the
block.

The emit loop below hands i_size_read(inode) to ocfs2_check_dir_entry(),
which refuses both an entry that close to the end and one whose rec_len
runs past it.  Apply the same two bounds to the re-validation scan, reading
i_size once into a local as ocfs2_check_dir_entry() takes it as @size.

Unlike the extent case there is no mask to corrupt here: an unbounded i
only sets ctx->pos past i_size, which ends the readdir early rather
than moving it to the wrong place.

Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
---
 fs/ocfs2/dir.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
index 39ce60874e17..863c69dec7da 100644
--- a/fs/ocfs2/dir.c
+++ b/fs/ocfs2/dir.c
@@ -1812,7 +1812,12 @@ static int ocfs2_dir_foreach_blk_id(struct inode *inode,
 		 * dirent right now.  Scan from the start of the block
 		 * to make sure. */
 		if (!inode_eq_iversion(inode, *f_version)) {
-			for (i = 0; i < i_size_read(inode) && i < offset; ) {
+			loff_t size = i_size_read(inode);
+
+			for (i = 0; i + OCFS2_DIR_REC_LEN(1) <= size &&
+			     i < offset;) {
+				unsigned int rec_len;
+
 				de = (struct ocfs2_dir_entry *)
 					(data->id_data + i);
 				/* It's too expensive to do a full
@@ -1821,10 +1826,11 @@ static int ocfs2_dir_foreach_blk_id(struct inode *inode,
 				 * least that it is non-zero.  A
 				 * failure will be detected in the
 				 * dirent test below. */
-				if (le16_to_cpu(de->rec_len) <
-				    OCFS2_DIR_REC_LEN(1))
+				rec_len = le16_to_cpu(de->rec_len);
+				if (rec_len < OCFS2_DIR_REC_LEN(1) ||
+				    i + rec_len > size)
 					break;
-				i += le16_to_cpu(de->rec_len);
+				i += rec_len;
 			}
 			ctx->pos = offset = i;
 			*f_version = inode_query_iversion(inode);
-- 
2.43.0