thermal/core: Potential buffer overflow in thermal_build_list_of_policies()

[ Upstream commit 1bb30b20b49773369c299d4d6c65227201328663 ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index f526ce31f5a2fcf7d3af7e22c429ca8b477f334d..20eab56b02cb93038bf3e9a9da2d6c25762f661f 100644 (file)
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -228,15 +228,14 @@ 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);