FAILED: patch "[PATCH] stm class: Fix channel bitmap on 32-bit systems" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 51e0f227812ed81a368de54157ebe14396b4be03 Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <[email protected]>
Date: Wed, 17 Apr 2019 10:35:35 +0300
Subject: [PATCH] stm class: Fix channel bitmap on 32-bit systems

Commit 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace Module devices") naively calculates the channel bitmap size in 64-bit chunks regardless of the size of underlying unsigned long, making the bitmap half as big on a 32-bit system. This leads to an out of bounds access with the upper half of the bitmap.

Fix this by using BITS_TO_LONGS. While at it, convert to using struct_size() for the total size calculation of the master struct.

index 5b5807cbcf7c..e55b902560de 100644
@@ -166,11 +166,10 @@ stm_master(struct stm_device *stm, unsigned int idx)
 static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
 {
 	struct stp_master *master;
-	size_t size;
 
-	size = ALIGN(stm->data->sw_nchannels, 8) / 8;
-	size += sizeof(struct stp_master);
-	master = kzalloc(size, GFP_ATOMIC);
+	master = kzalloc(struct_size(master, chan_map,
+				     BITS_TO_LONGS(stm->data->sw_nchannels)),
+			 GFP_ATOMIC);
 	if (!master)
 		return -ENOMEM;