[PATCH v4] 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 record size and use a reusable B-tree node
range helper to reject invalid write parameters before calling
hfs_bnode_write(). This prevents an invalid update from being treated
as successful and avoids clearing HFS_FLG_EXT_DIRTY in that case.

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>

Sorry, I missed your suggestion about factoring the validation into a
reusable helper in v3. This revision addresses it.

Changes in v4:
- Factor B-tree node range validation into a reusable helper, as
  suggested by Viacheslav Dubeyko.
- Keep the extent-record size check local to the extent write path.
- Preserve the error propagation and validation behavior from v3.

---
 fs/hfs/btree.h  |  7 +++++++
 fs/hfs/extent.c | 12 ++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/fs/hfs/btree.h b/fs/hfs/btree.h
index b4c3f2a31471..576412e6901e 100644
--- a/fs/hfs/btree.h
+++ b/fs/hfs/btree.h
@@ -84,6 +84,13 @@ struct hfs_find_data {
 	int entryoffset, entrylength;
 };
 
+static inline bool hfs_bnode_is_valid_range(struct hfs_bnode *node,
+					    int off, int len)
+{
+	return off >= 0 && len > 0 &&
+	       (u64)off + len <= 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..ece782205b47 100644
--- a/fs/hfs/extent.c
+++ b/fs/hfs/extent.c
@@ -121,12 +121,20 @@ 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 (fd->entrylength != sizeof(hfs_extent_rec) ||
+		    !hfs_bnode_is_valid_range(fd->bnode, fd->entryoffset,
+					      fd->entrylength))
+			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