Re: [PATCH] vfio: Fix smatch errors in vfio_combine_iova_ranges()

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On 10/2/2023 3:43 PM, Alex Williamson wrote:
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smatch reports:

vfio_combine_iova_ranges() error: uninitialized symbol 'last'.
vfio_combine_iova_ranges() error: potentially dereferencing uninitialized 'comb_end'.
vfio_combine_iova_ranges() error: potentially dereferencing uninitialized 'comb_start'.

These errors are only reachable via invalid input, in the case of
@last when we receive an empty rb-tree or for @comb_{start,end} if the
rb-tree is empty or otherwise fails to produce a second node that
reduces the gap.  Add tests with warnings for these cases.

Reported-by: Cong Liu <liucong2@xxxxxxxxxx>
Link: https://lore.kernel.org/all/20230920095532.88135-1-liucong2@xxxxxxxxxx
Cc: Yishai Hadas <yishaih@xxxxxxxxxx>
Cc: Brett Creeley <brett.creeley@xxxxxxx>
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
  drivers/vfio/vfio_main.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 40732e8ed4c6..e31e1952d7b8 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -946,6 +946,11 @@ void vfio_combine_iova_ranges(struct rb_root_cached *root, u32 cur_nodes,
                 unsigned long last;

                 comb_start = interval_tree_iter_first(root, 0, ULONG_MAX);
+
+               /* Empty list */
+               if (WARN_ON_ONCE(!comb_start))
+                       return;
+
                 curr = comb_start;
                 while (curr) {
                         last = curr->last;
@@ -975,6 +980,11 @@ void vfio_combine_iova_ranges(struct rb_root_cached *root, u32 cur_nodes,
                         prev = curr;
                         curr = interval_tree_iter_next(curr, 0, ULONG_MAX);
                 }
+
+               /* Empty list or no nodes to combine */
+               if (WARN_ON_ONCE(min_gap == ULONG_MAX))
+                       break;
+
                 comb_start->last = comb_end->last;
                 interval_tree_remove(comb_end, root);
                 cur_nodes--;
--
2.40.1


LGTM. Thanks for fixing this.

Reviewed-by: Brett Creeley <brett.creeley@xxxxxxx>



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