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 2db83b555e594f45ba90ef00c75debe71e9777ee..94820f25a15ffab8d5a19925a1b5ae9da1104732 100644 (file)
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -231,15 +231,14 @@ 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);