[PATCH] cgroup/misc: Fix an overflow

[Haitao Huang]

The variable 'new_usage' in misc_cg_try_charge() may overflow if it
becomes above INT_MAX. This was observed when I implement the new SGX
EPC cgroup[1] as a misc cgroup and test on a platform with large SGX EPC
sizes.

Change type of new_usage to long from int and check overflow.

Fixes: a72232eabdfcf ("cgroup: Add misc cgroup controller")
Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>

[1] https://lore.kernel.org/linux-sgx/20230712230202.47929-1-haitao.huang@xxxxxxxxxxxxxxx/
---
 kernel/cgroup/misc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
index fe3e8a0eb7ed..ff9f900981a3 100644
--- a/kernel/cgroup/misc.c
+++ b/kernel/cgroup/misc.c
@@ -143,7 +143,7 @@ int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg,
 	struct misc_cg *i, *j;
 	int ret;
 	struct misc_res *res;
-	int new_usage;
+	long new_usage;
 
 	if (!(valid_type(type) && cg && READ_ONCE(misc_res_capacity[type])))
 		return -EINVAL;
@@ -153,10 +153,10 @@ int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg,
 
 	for (i = cg; i; i = parent_misc(i)) {
 		res = &i->res[type];
-
 		new_usage = atomic_long_add_return(amount, &res->usage);
 		if (new_usage > READ_ONCE(res->max) ||
-		    new_usage > READ_ONCE(misc_res_capacity[type])) {
+		    new_usage > READ_ONCE(misc_res_capacity[type]) ||
+		    new_usage < 0) {
 			ret = -EBUSY;
 			goto err_charge;
 		}
-- 
2.25.1