linux-ext4 - [PATCH 6/7] libext2fs: check for cyclic loops in the extent tree

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Message-Id: <20220607042444.1798015-7-tytso@mit.edu>
Date:   Tue,  7 Jun 2022 00:24:43 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     Nils Bars <nils.bars@....de>,
        Moritz Schlögel <moritz.schloegel@....de>,
        Nico Schiller <nico.schiller@....de>,
        "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 6/7] libext2fs: check for cyclic loops in the extent tree

In the extent tree handling code in libext2fs, when we go move down
the extent tree, if a cyclic loop is detected, return an error.

Reported-by: Nils Bars <nils.bars@....de>
Reported-by: Moritz Schlögel <moritz.schloegel@....de>
Reported-by: Nico Schiller <nico.schiller@....de>
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 lib/ext2fs/ext2_err.et.in |  3 +++
 lib/ext2fs/extent.c       | 11 +++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/lib/ext2fs/ext2_err.et.in b/lib/ext2fs/ext2_err.et.in
index cf0e00ea..bb1dcf14 100644
--- a/lib/ext2fs/ext2_err.et.in
+++ b/lib/ext2fs/ext2_err.et.in
@@ -551,4 +551,7 @@ ec	EXT2_ET_NO_GDESC,
 ec	EXT2_FILSYS_CORRUPTED,
 	"The internal ext2_filsys data structure appears to be corrupted"
 
+ec	EXT2_ET_EXTENT_CYCLE,
+	"Found cyclic loop in extent tree"
+
 	end
diff --git a/lib/ext2fs/extent.c b/lib/ext2fs/extent.c
index 1a206a16..82e75ccd 100644
--- a/lib/ext2fs/extent.c
+++ b/lib/ext2fs/extent.c
@@ -47,6 +47,7 @@ struct extent_path {
 	int		visit_num;
 	int		flags;
 	blk64_t		end_blk;
+	blk64_t		blk;
 	void		*curr;
 };
 
@@ -286,6 +287,7 @@ errcode_t ext2fs_extent_open2(ext2_filsys fs, ext2_ino_t ino,
 	handle->path[0].end_blk =
 		(EXT2_I_SIZE(handle->inode) + fs->blocksize - 1) >>
 		 EXT2_BLOCK_SIZE_BITS(fs->super);
+	handle->path[0].blk = 0;
 	handle->path[0].visit_num = 1;
 	handle->level = 0;
 	handle->magic = EXT2_ET_MAGIC_EXTENT_HANDLE;
@@ -305,14 +307,14 @@ errout:
 errcode_t ext2fs_extent_get(ext2_extent_handle_t handle,
 			    int flags, struct ext2fs_extent *extent)
 {
-	struct extent_path	*path, *newpath;
+	struct extent_path	*path, *newpath, *tp;
 	struct ext3_extent_header	*eh;
 	struct ext3_extent_idx		*ix = 0;
 	struct ext3_extent		*ex;
 	errcode_t			retval;
 	blk64_t				blk;
 	blk64_t				end_blk;
-	int				orig_op, op;
+	int				orig_op, op, l;
 	int				failed_csum = 0;
 
 	EXT2_CHECK_MAGIC(handle, EXT2_ET_MAGIC_EXTENT_HANDLE);
@@ -467,6 +469,11 @@ retry:
 		}
 		blk = ext2fs_le32_to_cpu(ix->ei_leaf) +
 			((__u64) ext2fs_le16_to_cpu(ix->ei_leaf_hi) << 32);
+		for (l = handle->level, tp = path; l > 0; l--, tp--) {
+			if (blk == tp->blk)
+				return EXT2_ET_EXTENT_CYCLE;
+		}
+		newpath->blk = blk;
 		if ((handle->fs->flags & EXT2_FLAG_IMAGE_FILE) &&
 		    (handle->fs->io != handle->fs->image_io))
 			memset(newpath->buf, 0, handle->fs->blocksize);
-- 
2.31.0