ipc: fix ipc data structures inconsistency

As described in the title, this patch fixes <ipc>id_ds inconsistency when
<ipc>ctl_stat executes concurrently with some ds-changing function, e.g.
shmat, msgsnd or whatever.

For instance, if shmctl(IPC_STAT) is running concurrently
with shmat, following data structure can be returned:
{... shm_lpid = 0, shm_nattch = 1, ...}

Link: http://lkml.kernel.org/r/20171202153456.6514-1-philippe.mikoyan@skat.systems
Signed-off-by: Philippe Mikoyan <philippe.mikoyan@skat.systems>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 6 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 1bbc029..0dcc669 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -476,9 +476,9 @@ static int msgctl_info(struct ipc_namespace *ns, int msqid,
 static int msgctl_stat(struct ipc_namespace *ns, int msqid,
 			 int cmd, struct msqid64_ds *p)
 {
-	int err;
 	struct msg_queue *msq;
-	int success_return;
+	int id = 0;
+	int err;
 
 	memset(p, 0, sizeof(*p));
 
@@ -489,14 +489,13 @@ static int msgctl_stat(struct ipc_namespace *ns, int msqid,
 			err = PTR_ERR(msq);
 			goto out_unlock;
 		}
-		success_return = msq->q_perm.id;
+		id = msq->q_perm.id;
 	} else {
 		msq = msq_obtain_object_check(ns, msqid);
 		if (IS_ERR(msq)) {
 			err = PTR_ERR(msq);
 			goto out_unlock;
 		}
-		success_return = 0;
 	}
 
 	err = -EACCES;
@@ -507,6 +506,14 @@ static int msgctl_stat(struct ipc_namespace *ns, int msqid,
 	if (err)
 		goto out_unlock;
 
+	ipc_lock_object(&msq->q_perm);
+
+	if (!ipc_valid_object(&msq->q_perm)) {
+		ipc_unlock_object(&msq->q_perm);
+		err = -EIDRM;
+		goto out_unlock;
+	}
+
 	kernel_to_ipc64_perm(&msq->q_perm, &p->msg_perm);
 	p->msg_stime  = msq->q_stime;
 	p->msg_rtime  = msq->q_rtime;
@@ -516,9 +523,10 @@ static int msgctl_stat(struct ipc_namespace *ns, int msqid,
 	p->msg_qbytes = msq->q_qbytes;
 	p->msg_lspid  = msq->q_lspid;
 	p->msg_lrpid  = msq->q_lrpid;
-	rcu_read_unlock();
 
-	return success_return;
+	ipc_unlock_object(&msq->q_perm);
+	rcu_read_unlock();
+	return id;
 
 out_unlock:
 	rcu_read_unlock();