[PATCH v2 1/1] cxl/region: Fix out-of-bounds access in cxl_cancel_auto_attach()

[Li Ming]

In cxl_cancel_auto_attach(), it assumes cxled->pos is a valid index for
accessing p->targets[]. However, cxled->pos can be set to negative errno
in cxl_region_sort_targets() if cxl_calc_interleave_pos() fails. This
causes the driver to use a negative index to access p->targets[],
resulting in out-of-bounds access.

Fix it by walking p->targets[] instead of using cxled->pos directly.

Fixes: 87805c32e6ad ("cxl/region: Fix use-after-free from auto assembly failure")
Signed-off-by: Li Ming <ming.li@xxxxxxxxxxxx>
---
Changes from v1:
- Update commit log. (Dave)
- Update comment in cxl_region_sort_targets(). (Dave)
- Fix potential 'hole' issue. (Alison & Sashiko review)
---
 drivers/cxl/core/region.c | 40 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index e50dc716d4e8..8956b049c462 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2011,8 +2011,9 @@ static int cxl_region_sort_targets(struct cxl_region *cxlr)
 		cxled->pos = cxl_calc_interleave_pos(cxled, &cxlr->hpa_range);
 		/*
 		 * Record that sorting failed, but still continue to calc
-		 * cxled->pos so that follow-on code paths can reliably
-		 * do p->targets[cxled->pos] to self-reference their entry.
+		 * cxled->pos so that cxl_calc_interleave_pos() emits its
+		 * dev_dbg() for every member. which is useful for auto
+		 * discovery debug.
 		 */
 		if (cxled->pos < 0)
 			rc = -ENXIO;
@@ -2202,18 +2203,30 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 	return 0;
 }
 
-static int cxl_region_by_target(struct device *dev, const void *data)
+static int cxl_region_remove_target(struct device *dev, void *data)
 {
-	const struct cxl_endpoint_decoder *cxled = data;
+	struct cxl_endpoint_decoder *cxled = data;
 	struct cxl_region_params *p;
 	struct cxl_region *cxlr;
+	int i;
 
 	if (!is_cxl_region(dev))
 		return 0;
 
 	cxlr = to_cxl_region(dev);
 	p = &cxlr->params;
-	return p->targets[cxled->pos] == cxled;
+	for (i = 0; i < p->interleave_ways; i++) {
+		if (p->targets[i] == cxled) {
+			p->nr_targets--;
+			cxled->state = CXL_DECODER_STATE_AUTO;
+			cxled->pos = -1;
+			p->targets[i] = NULL;
+
+			return 1;
+		}
+	}
+
+	return 0;
 }
 
 /*
@@ -2222,25 +2235,10 @@ static int cxl_region_by_target(struct device *dev, const void *data)
  */
 static void cxl_cancel_auto_attach(struct cxl_endpoint_decoder *cxled)
 {
-	struct cxl_region_params *p;
-	struct cxl_region *cxlr;
-	int pos = cxled->pos;
-
 	if (cxled->state != CXL_DECODER_STATE_AUTO_STAGED)
 		return;
 
-	struct device *dev __free(put_device) =
-		bus_find_device(&cxl_bus_type, NULL, cxled, cxl_region_by_target);
-	if (!dev)
-		return;
-
-	cxlr = to_cxl_region(dev);
-	p = &cxlr->params;
-
-	p->nr_targets--;
-	cxled->state = CXL_DECODER_STATE_AUTO;
-	cxled->pos = -1;
-	p->targets[pos] = NULL;
+	bus_for_each_dev(&cxl_bus_type, NULL, cxled, cxl_region_remove_target);
 }
 
 static struct cxl_region *
-- 
2.43.0