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>

4 files changed, 43 insertions, 12 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 1bbc029d2b17..0dcc6699dc53 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();
diff --git a/ipc/sem.c b/ipc/sem.c
index 87bd38f38dc3..a4af04979fd2 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;
 
diff --git a/ipc/shm.c b/ipc/shm.c
index 7acda23430aa..4643865e9171 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -909,9 +909,11 @@ static int shmctl_stat(struct ipc_namespace *ns, int shmid,
                         int cmd, struct shmid64_ds *tbuf)
 {
         struct shmid_kernel *shp;
-        int result;
+        int id = 0;
         int err;
 
+        memset(tbuf, 0, sizeof(*tbuf));
+
         rcu_read_lock();
         if (cmd == SHM_STAT) {
                 shp = shm_obtain_object(ns, shmid);
@@ -919,14 +921,13 @@ static int shmctl_stat(struct ipc_namespace *ns, int shmid,
                         err = PTR_ERR(shp);
                         goto out_unlock;
                 }
-                result = shp->shm_perm.id;
+                id = shp->shm_perm.id;
         } else {
                 shp = shm_obtain_object_check(ns, shmid);
                 if (IS_ERR(shp)) {
                         err = PTR_ERR(shp);
                         goto out_unlock;
                 }
-                result = 0;
         }
 
         err = -EACCES;
@@ -937,7 +938,14 @@ static int shmctl_stat(struct ipc_namespace *ns, int shmid,
         if (err)
                 goto out_unlock;
 
-        memset(tbuf, 0, sizeof(*tbuf));
+        ipc_lock_object(&shp->shm_perm);
+
+        if (!ipc_valid_object(&shp->shm_perm)) {
+                ipc_unlock_object(&shp->shm_perm);
+                err = -EIDRM;
+                goto out_unlock;
+        }
+
         kernel_to_ipc64_perm(&shp->shm_perm, &tbuf->shm_perm);
         tbuf->shm_segsz = shp->shm_segsz;
         tbuf->shm_atime = shp->shm_atim;
@@ -946,8 +954,10 @@ static int shmctl_stat(struct ipc_namespace *ns, int shmid,
         tbuf->shm_cpid  = shp->shm_cprid;
         tbuf->shm_lpid  = shp->shm_lprid;
         tbuf->shm_nattch = shp->shm_nattch;
+
+        ipc_unlock_object(&shp->shm_perm);
         rcu_read_unlock();
-        return result;
+        return id;
 
 out_unlock:
         rcu_read_unlock();
diff --git a/ipc/util.c b/ipc/util.c
index ff045fec8d83..4ed5a17dd06f 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -23,9 +23,12 @@
  *          tree.
  *          - perform initial checks (capabilities, auditing and permission,
  *            etc).
- *          - perform read-only operations, such as STAT, INFO commands.
+ *          - perform read-only operations, such as INFO command, that
+ *            do not demand atomicity
  *            acquire the ipc lock (kern_ipc_perm.lock) through
  *            ipc_lock_object()
+ *              - perform read-only operations that demand atomicity,
+ *                such as STAT command.
  *              - perform data updates, such as SET, RMID commands and
  *                mechanism-specific operations (semop/semtimedop,
  *                msgsnd/msgrcv, shmat/shmdt).