From bf7cbaae0831252b416f375ca9b1027ecd4642dd Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Date: Thu, 21 Feb 2019 14:19:17 +0200
Subject: [PATCH] stm class: Prevent division by zero
Git-commit: bf7cbaae0831252b416f375ca9b1027ecd4642dd
Patch-mainline: v5.1-rc1
References: bsc#1051510

Using STP_POLICY_ID_SET ioctl command with dummy_stm device, or any STM
device that supplies zero mmio channel size, will trigger a division by
zero bug in the kernel.

Prevent this by disallowing channel widths other than 1 for such devices.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Fixes: 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace Module devices")
Cc: stable@vger.kernel.org # v4.4+
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/hwtracing/stm/core.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -561,7 +561,7 @@ static int stm_char_policy_set_ioctl(str
 {
 	struct stm_device *stm = stmf->stm;
 	struct stp_policy_id *id;
-	int ret = -EINVAL;
+	int ret = -EINVAL, wlimit = 1;
 	u32 size;
 
 	if (stmf->output.nr_chans)
@@ -589,8 +589,10 @@ static int stm_char_policy_set_ioctl(str
 	if (id->__reserved_0 || id->__reserved_1)
 		goto err_free;
 
-	if (id->width < 1 ||
-	    id->width > PAGE_SIZE / stm->data->sw_mmiosz)
+	if (stm->data->sw_mmiosz)
+		wlimit = PAGE_SIZE / stm->data->sw_mmiosz;
+
+	if (id->width < 1 || id->width > wlimit)
 		goto err_free;
 
 	ret = stm_file_assign(stmf, id->id, id->width);