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, 10 insertions, 0 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 87bd38f..a4af049 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1213,10 +1213,20 @@ static int semctl_stat(struct ipc_namespace *ns, int semid,
 	if (err)
 		goto out_unlock;
 
+	ipc_lock_object(&sma->sem_perm);
+
+	if (!ipc_valid_object(&sma->sem_perm)) {
+		ipc_unlock_object(&sma->sem_perm);
+		err = -EIDRM;
+		goto out_unlock;
+	}
+
 	kernel_to_ipc64_perm(&sma->sem_perm, &semid64->sem_perm);
 	semid64->sem_otime = get_semotime(sma);
 	semid64->sem_ctime = sma->sem_ctime;
 	semid64->sem_nsems = sma->sem_nsems;
+
+	ipc_unlock_object(&sma->sem_perm);
 	rcu_read_unlock();
 	return id;