ipc/util.c: use ipc_rcu_putref() for failues in ipc_addid()

ipc_addid() is impossible to use:
- for certain failures, the caller must not use ipc_rcu_putref(),
  because the reference counter is not yet initialized.
- for other failures, the caller must use ipc_rcu_putref(),
  because parallel operations could be ongoing already.

The patch cleans that up, by initializing the refcount early, and by
modifying all callers.

The issues is related to the finding of
syzbot+2827ef6b3385deb07eaf@syzkaller.appspotmail.com: syzbot found an
issue with reading kern_ipc_perm.seq, here both read and write to already
released memory could happen.

Link: http://lkml.kernel.org/r/20180712185241.4017-4-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 7cb89a9b24e2..3132aa27ff88 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -163,7 +163,7 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
 	/* ipc_addid() locks msq upon success. */
 	retval = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
 	if (retval < 0) {
-		call_rcu(&msq->q_perm.rcu, msg_rcu_free);
+		ipc_rcu_putref(&msq->q_perm, msg_rcu_free);
 		return retval;
 	}