From c91ed3a5c2ab82c99ba07b99a569a6247ad47935 Mon Sep 17 00:00:00 2001 From: John Sperbeck Date: Sun, 21 May 2023 19:29:53 +0000 Subject: [PATCH] cgroup: always put cset in cgroup_css_set_put_fork commit 2bd110339288c18823dcace602b63b0d8627e520 upstream. 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@vger.kernel.org # v5.7+ Signed-off-by: John Sperbeck Signed-off-by: Tejun Heo [TJM: This backport accommodates the lack of cgroup_unlock] Signed-off-by: T.J. Mercier Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup/cgroup.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index a92990f070d1..edae2f49f73f 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -6259,19 +6259,18 @@ 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 (cset) { + put_css_set(cset); + kargs->cset = NULL; + } + if (kargs->flags & CLONE_INTO_CGROUP) { - struct cgroup *cgrp = kargs->cgrp; - struct css_set *cset = kargs->cset; - mutex_unlock(&cgroup_mutex); - - if (cset) { - put_css_set(cset); - kargs->cset = NULL; - } - if (cgrp) { cgroup_put(cgrp); kargs->cgrp = NULL;