[PATCH v5] hfs: handle extent B-tree write errors

[Davy Felipe <davyfelipe34@gmail.com>]

hfs_brec_insert() may fail while inserting a new extent record, but
__hfs_ext_write_extent() currently ignores its return value and clears
HFS_FLG_EXT_DIRTY and HFS_FLG_EXT_NEW as if the insertion had
succeeded.

Propagate errors returned by hfs_brec_insert() and only clear the
extent flags after a successful insertion.

When updating an existing extent record, hfs_bnode_write() returns
void. Validate the extent write parameters before calling it so an
invalid update is reported as -EIO instead of being treated as
successful.

Use a reusable B-tree node range helper that takes the find data and
the expected record size. The helper validates the bnode and tree
pointers, entry offset and entry length, and ensures that the write
range fits within the node.

Negative-path testing in QEMU confirmed that an insertion error is
propagated to the caller. Testing the existing-record path also
confirmed that invalid write parameters are rejected before
HFS_FLG_EXT_DIRTY is cleared.

Signed-off-by: Davy Felipe <davyfelipe34@gmail.com>
Thanks for the feedback. I updated the helper to take struct
hfs_find_data and the expected entry size so the bnode/tree,
entry offset and entry length validation stay in one place.

Changes in v5:
- Pass struct hfs_find_data to hfs_bnode_is_valid_range().
- Validate the bnode and tree pointers in the helper.
- Pass the expected entry size and validate fd->entrylength there.
- Simplify the extent write path to a single validation helper call.

---
 fs/hfs/btree.h  | 19 +++++++++++++++++++
 fs/hfs/extent.c | 10 ++++++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/hfs/btree.h b/fs/hfs/btree.h
index b4c3f2a31471..ab7a7c65a126 100644
--- a/fs/hfs/btree.h
+++ b/fs/hfs/btree.h
@@ -84,6 +84,25 @@ struct hfs_find_data {
 	int entryoffset, entrylength;
 };
 
+static inline bool hfs_bnode_is_valid_range(struct hfs_find_data *fd, int expected_len)
+{
+	struct hfs_bnode *node;
+
+	if (!fd)
+		return false;
+
+	node = fd->bnode;
+	if (!node || !node->tree)
+		return false;
+
+	if (expected_len <= 0 || fd->entryoffset < 0 ||
+	    fd->entrylength != expected_len)
+		return false;
+
+	return (u64)fd->entryoffset + fd->entrylength <=
+	       node->tree->node_size;
+}
+
 
 /* btree.c */
 extern struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id,
diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c
index f066a99a863b..4d65943d1117 100644
--- a/fs/hfs/extent.c
+++ b/fs/hfs/extent.c
@@ -121,12 +121,18 @@ static int __hfs_ext_write_extent(struct inode *inode, struct hfs_find_data *fd)
 		res = hfs_bmap_reserve(fd->tree, fd->tree->depth + 1);
 		if (res)
 			return res;
-		hfs_brec_insert(fd, HFS_I(inode)->cached_extents, sizeof(hfs_extent_rec));
+		res = hfs_brec_insert(fd, HFS_I(inode)->cached_extents,
+				      sizeof(hfs_extent_rec));
+		if (res)
+			return res;
 		HFS_I(inode)->flags &= ~(HFS_FLG_EXT_DIRTY|HFS_FLG_EXT_NEW);
 	} else {
 		if (res)
 			return res;
-		hfs_bnode_write(fd->bnode, HFS_I(inode)->cached_extents, fd->entryoffset, fd->entrylength);
+		if (!hfs_bnode_is_valid_range(fd, sizeof(hfs_extent_rec)))
+			return -EIO;
+		hfs_bnode_write(fd->bnode, HFS_I(inode)->cached_extents,
+				fd->entryoffset, fd->entrylength);
 		HFS_I(inode)->flags &= ~HFS_FLG_EXT_DIRTY;
 	}
 	return 0;
-- 
2.55.0