[PATCH v3] vfio: Fix uninitialized symbol and potential dereferencing errors in vfio_combine_iova_ranges

[Cong Liu]

when compiling with smatch check, the following errors were encountered:

drivers/vfio/vfio_main.c:957 vfio_combine_iova_ranges() error: uninitialized symbol 'last'.
drivers/vfio/vfio_main.c:978 vfio_combine_iova_ranges() error: potentially dereferencing uninitialized 'comb_end'.
drivers/vfio/vfio_main.c:978 vfio_combine_iova_ranges() error: potentially dereferencing uninitialized 'comb_start'.

This patch initializes the variables last, comb_end, and comb_start
to avoid compiler warnings and add proper argument checks to ensure
interval_tree_iter_first() does not return NULL.

Signed-off-by: Cong Liu <liucong2@xxxxxxxxxx>
---
 drivers/vfio/vfio_main.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 40732e8ed4c6..ecd4dd8e6b05 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -938,12 +938,17 @@ static int vfio_ioctl_device_feature_migration(struct vfio_device *device,
 void vfio_combine_iova_ranges(struct rb_root_cached *root, u32 cur_nodes,
 			      u32 req_nodes)
 {
-	struct interval_tree_node *prev, *curr, *comb_start, *comb_end;
+	if (!cur_nodes || cur_nodes <= req_nodes ||
+		WARN_ON(!req_nodes || !root->rb_root.rb_node))
+		return;
+
+	struct interval_tree_node *prev, *curr;
+	struct interval_tree_node *comb_start = NULL, *comb_end = NULL;
 	unsigned long min_gap, curr_gap;
 
 	/* Special shortcut when a single range is required */
 	if (req_nodes == 1) {
-		unsigned long last;
+		unsigned long last = 0;
 
 		comb_start = interval_tree_iter_first(root, 0, ULONG_MAX);
 		curr = comb_start;
-- 
2.34.1