From: John Sperbeck jsperbeck@google.com
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 jsperbeck@google.com Signed-off-by: Tejun Heo tj@kernel.org Tested-by: T.J. Mercier tjmercier@google.com (cherry picked from commit 2bd110339288c18823dcace602b63b0d8627e520) [TJM: This backport accommodates the lack of cgroup_unlock] Signed-off-by: T.J. Mercier tjmercier@google.com --- 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 935e8121b21e..1605a6744458 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) { mutex_unlock(&cgroup_mutex); - - if (cset) { - put_css_set(cset); - kargs->cset = NULL; - } - if (cgrp) { cgroup_put(cgrp); kargs->cgrp = NULL;