stm class: Prevent user-controllable allocations

[Pavel Machek]

It seems to me that we still allow overflow if count == ~0. We'll then
allocate 0 bytes but copy ~0 bytes. That does not sound healthy.

Fixes: f08b18266c7116e2ec6885dd53a928f580060a71

Signed-off-by: Pavel Machek <pavel@xxxxxxx>

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index c7ba8ac..8846fca 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
 	char *kbuf;
 	int err;
 
-	if (count + 1 > PAGE_SIZE)
+	if (count > PAGE_SIZE - 1)
 		count = PAGE_SIZE - 1;
 
 	/*

-- 
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