Patch "cgroup: always put cset in cgroup_css_set_put_fork" has been added to the 6.3-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    cgroup: always put cset in cgroup_css_set_put_fork

to the 6.3-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-always-put-cset-in-cgroup_css_set_put_fork.patch
and it can be found in the queue-6.3 subdirectory.

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



commit 1a1986781f4a86ea4a6975b454d70dd368584db2
Author: John Sperbeck <jsperbeck@xxxxxxxxxx>
Date:   Sun May 21 19:29:53 2023 +0000

    cgroup: always put cset in cgroup_css_set_put_fork
    
    [ Upstream commit 2bd110339288c18823dcace602b63b0d8627e520 ]
    
    A successful call to cgroup_css_set_fork() will always have taken
    a ref on kargs->cset (regardless of CLONE_INTO_CGROUP), so always
    do a corresponding put in cgroup_css_set_put_fork().
    
    Without this, a cset and its contained css structures will be
    leaked for some fork failures.  The following script reproduces
    the leak for a fork failure due to exceeding pids.max in the
    pids controller.  A similar thing can happen if we jump to the
    bad_fork_cancel_cgroup label in copy_process().
    
    [ -z "$1" ] && echo "Usage $0 pids-root" && exit 1
    PID_ROOT=$1
    CGROUP=$PID_ROOT/foo
    
    [ -e $CGROUP ] && rmdir -f $CGROUP
    mkdir $CGROUP
    echo 5 > $CGROUP/pids.max
    echo $$ > $CGROUP/cgroup.procs
    
    fork_bomb()
    {
            set -e
            for i in $(seq 10); do
                    /bin/sleep 3600 &
            done
    }
    
    (fork_bomb) &
    wait
    echo $$ > $PID_ROOT/cgroup.procs
    kill $(cat $CGROUP/cgroup.procs)
    rmdir $CGROUP
    
    Fixes: ef2c41cf38a7 ("clone3: allow spawning processes into cgroups")
    Cc: stable@xxxxxxxxxxxxxxx # v5.7+
    Signed-off-by: John Sperbeck <jsperbeck@xxxxxxxxxx>
    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 83ea13f2ccb1d..fd57c1dca1ccf 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6476,19 +6476,18 @@ static int cgroup_css_set_fork(struct kernel_clone_args *kargs)
 static void cgroup_css_set_put_fork(struct kernel_clone_args *kargs)
 	__releases(&cgroup_threadgroup_rwsem) __releases(&cgroup_mutex)
 {
+	struct cgroup *cgrp = kargs->cgrp;
+	struct css_set *cset = kargs->cset;
+
 	cgroup_threadgroup_change_end(current);
 
-	if (kargs->flags & CLONE_INTO_CGROUP) {
-		struct cgroup *cgrp = kargs->cgrp;
-		struct css_set *cset = kargs->cset;
+	if (cset) {
+		put_css_set(cset);
+		kargs->cset = NULL;
+	}
 
+	if (kargs->flags & CLONE_INTO_CGROUP) {
 		cgroup_unlock();
-
-		if (cset) {
-			put_css_set(cset);
-			kargs->cset = NULL;
-		}
-
 		if (cgrp) {
 			cgroup_put(cgrp);
 			kargs->cgrp = NULL;