thermal/core: Potential buffer overflow in thermal_build_list_of_policies()

After printing the list of thermal governors, then this function prints
a newline character.  The problem is that "size" has not been updated
after printing the last governor.  This means that it can write one
character (the NUL terminator) beyond the end of the buffer.

Get rid of the "size" variable and just use "PAGE_SIZE - count" directly.

Fixes: 1b4f48494eb2 ("thermal: core: group functions related to governor handling")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210916131342.GB25094@kili

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 97ef9b040b84a95e82bd6c691f4bb87004c26ade..51374f4e1ccafadeb4ad4fd6ae7545092cd370d4 100644 (file)
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -222,15 +222,14 @@ int thermal_build_list_of_policies(char *buf)
 {
        struct thermal_governor *pos;
        ssize_t count = 0;
-       ssize_t size = PAGE_SIZE;
 
        mutex_lock(&thermal_governor_lock);
 
        list_for_each_entry(pos, &thermal_governor_list, governor_list) {
-               size = PAGE_SIZE - count;
-               count += scnprintf(buf + count, size, "%s ", pos->name);
+               count += scnprintf(buf + count, PAGE_SIZE - count, "%s ",
+                                  pos->name);
        }
-       count += scnprintf(buf + count, size, "\n");
+       count += scnprintf(buf + count, PAGE_SIZE - count, "\n");
 
        mutex_unlock(&thermal_governor_lock);