[PATCH v2] image-fit: Limit recursion depth in fdt_check_no_at()

[Anton Ivanov]

From: Binarly Vulnerability Research <vr at binarly.io>

fdt_check_no_at() recurses into every subnode without a depth
limit. A deeply nested FIT image can exhaust the stack and crash
U-Boot.

Add a depth check using FDT_MAX_DEPTH to bound the recursion.

Signed-off-by: Binarly Vulnerability Research <vr at binarly.io>
---
Changes in v2:
- Rewrite commit message to be concise per maintainer feedback

 boot/image-fit.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/boot/image-fit.c b/boot/image-fit.c
index b0fcaf6e17f..0e225ecd0c2 100644
--- a/boot/image-fit.c
+++ b/boot/image-fit.c
@@ -41,6 +41,7 @@ DECLARE_GLOBAL_DATA_PTR;
 #include <bootm.h>
 #include <image.h>
 #include <bootstage.h>
+#include <fdt_region.h>
 #include <upl.h>
 #include <u-boot/crc.h>
 
@@ -1643,20 +1644,24 @@ int fit_image_check_comp(const void *fit, int noffset, uint8_t comp)
  *
  * @fit: FIT to check
  * @parent: Parent node to check
- * Return: 0 if OK, -EADDRNOTAVAIL is a node has a name containing '@'
+ * @depth: Current recursion depth
+ * Return: 0 if OK, or error value
  */
-static int fdt_check_no_at(const void *fit, int parent)
+static int fdt_check_no_at(const void *fit, int parent, int depth)
 {
 	const char *name;
 	int node;
 	int ret;
 
+	if (depth >= FDT_MAX_DEPTH)
+		return -FDT_ERR_BADSTRUCTURE;
+
 	name = fdt_get_name(fit, parent, NULL);
 	if (!name || strchr(name, '@'))
 		return -EADDRNOTAVAIL;
 
 	fdt_for_each_subnode(node, fit, parent) {
-		ret = fdt_check_no_at(fit, node);
+		ret = fdt_check_no_at(fit, node, depth + 1);
 		if (ret)
 			return ret;
 	}
@@ -1696,7 +1701,7 @@ int fit_check_format(const void *fit, ulong size)
 		 * attached. Protect against this by disallowing unit addresses.
 		 */
 		if (!ret && CONFIG_IS_ENABLED(FIT_SIGNATURE)) {
-			ret = fdt_check_no_at(fit, 0);
+			ret = fdt_check_no_at(fit, 0, 0);
 
 			if (ret) {
 				log_debug("FIT check error %d\n", ret);
-- 
2.53.0