[PATCH v1] liveupdate: sanitize incoming session count

[Li Chen <me@linux.beauty>]

luo_session_deserialize() iterates incoming sessions using
luo_session_header_ser::count. The header physical address is provided by
the previous kernel via the KHO FDT node.

If the header is corrupted, count may become arbitrarily large and the new
kernel can read past the preserved session array (sh->ser[i]). This is an
OOB read that can crash or hang early boot.

This can happen if the FDT node is corrupted or mis-parsed and points to a
wrong header address, if stale/incompatible handover data is interpreted
with the wrong layout, or if the preserved region is scribbled by memory
corruption or DMA after kexec.

Clamp the incoming count to LUO_SESSION_MAX before iterating.

Signed-off-by: Li Chen <me@linux.beauty>
---
 kernel/liveupdate/luo_session.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index dbdbc3bd7929..9d6c3ad990d9 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -515,6 +515,7 @@ int luo_session_deserialize(void)
 	struct luo_session_header *sh = &luo_session_global.incoming;
 	static bool is_deserialized;
 	static int err;
+	u64 count;
 
 	/* If has been deserialized, always return the same error code */
 	if (is_deserialized)
@@ -524,6 +525,13 @@ int luo_session_deserialize(void)
 	if (!sh->active)
 		return 0;
 
+	count = sh->header_ser->count;
+	if (count > LUO_SESSION_MAX) {
+		pr_warn("incoming session count %llu exceeds max %lu\n",
+			count, LUO_SESSION_MAX);
+		count = LUO_SESSION_MAX;
+	}
+
 	/*
 	 * Note on error handling:
 	 *
@@ -539,7 +547,7 @@ int luo_session_deserialize(void)
 	 * userspace to detect the failure and trigger a reboot, which will
 	 * reliably reset devices and reclaim memory.
 	 */
-	for (int i = 0; i < sh->header_ser->count; i++) {
+	for (u64 i = 0; i < count; i++) {
 		struct luo_session *session;
 
 		session = luo_session_alloc(sh->ser[i].name);
-- 
2.52.0