Patch "cgroup: Fix potential overflow issue when checking max_depth" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    cgroup: Fix potential overflow issue when checking max_depth

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cgroup-fix-potential-overflow-issue-when-checking-ma.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 88da2d06242f6999930e55a755e843cae1c76ecc
Author: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
Date:   Sat Oct 12 07:22:46 2024 +0000

    cgroup: Fix potential overflow issue when checking max_depth
    
    [ Upstream commit 3cc4e13bb1617f6a13e5e6882465984148743cf4 ]
    
    cgroup.max.depth is the maximum allowed descent depth below the current
    cgroup. If the actual descent depth is equal or larger, an attempt to
    create a new child cgroup will fail. However due to the cgroup->max_depth
    is of int type and having the default value INT_MAX, the condition
    'level > cgroup->max_depth' will never be satisfied, and it will cause
    an overflow of the level after it reaches to INT_MAX.
    
    Fix it by starting the level from 0 and using '>=' instead.
    
    It's worth mentioning that this issue is unlikely to occur in reality,
    as it's impossible to have a depth of INT_MAX hierarchy, but should be
    be avoided logically.
    
    Fixes: 1a926e0bbab8 ("cgroup: implement hierarchy limits")
    Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
    Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 16ae868941211..79e57b6df7316 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5502,7 +5502,7 @@ static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
 {
 	struct cgroup *cgroup;
 	int ret = false;
-	int level = 1;
+	int level = 0;
 
 	lockdep_assert_held(&cgroup_mutex);
 
@@ -5510,7 +5510,7 @@ static bool cgroup_check_hierarchy_limits(struct cgroup *parent)
 		if (cgroup->nr_descendants >= cgroup->max_descendants)
 			goto fail;
 
-		if (level > cgroup->max_depth)
+		if (level >= cgroup->max_depth)
 			goto fail;
 
 		level++;