[GIT PULL 7/7] stm class: Prevent division by zero

[Alexander Shishkin]

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

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index c80b064224f6..c7ba8acfd4d5 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -735,7 +735,7 @@ static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 	struct stm_device *stm = stmf->stm;
 	struct stp_policy_id *id;
 	char *ids[] = { NULL, NULL };
-	int ret = -EINVAL;
+	int ret = -EINVAL, wlimit = 1;
 	u32 size;
 
 	if (stmf->output.nr_chans)
@@ -763,8 +763,10 @@ static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
 	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;
 
 	ids[0] = id->id;
-- 
2.20.1