1 files changed, 29 insertions, 8 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index d69739610fd4..7a51443a51d6 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -208,15 +208,18 @@ static void shm_open(struct vm_area_struct *vma)
  */
 static void shm_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp)
 {
+	struct file *shm_file;
+
+	shm_file = shp->shm_file;
+	shp->shm_file = NULL;
 	ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	shm_rmid(ns, shp);
 	shm_unlock(shp);
-	if (!is_file_hugepages(shp->shm_file))
-		shmem_lock(shp->shm_file, 0, shp->mlock_user);
+	if (!is_file_hugepages(shm_file))
+		shmem_lock(shm_file, 0, shp->mlock_user);
 	else if (shp->mlock_user)
-		user_shm_unlock(file_inode(shp->shm_file)->i_size,
-						shp->mlock_user);
-	fput (shp->shm_file);
+		user_shm_unlock(file_inode(shm_file)->i_size, shp->mlock_user);
+	fput(shm_file);
 	ipc_rcu_putref(shp, shm_rcu_free);
 }
 
@@ -974,15 +977,25 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
 		ipc_lock_object(&shp->shm_perm);
 		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
 			kuid_t euid = current_euid();
-			err = -EPERM;
 			if (!uid_eq(euid, shp->shm_perm.uid) &&
-			    !uid_eq(euid, shp->shm_perm.cuid))
+			    !uid_eq(euid, shp->shm_perm.cuid)) {
+				err = -EPERM;
 				goto out_unlock0;
-			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
+			}
+			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK)) {
+				err = -EPERM;
 				goto out_unlock0;
+			}
 		}
 
 		shm_file = shp->shm_file;
+
+		/* check if shm_destroy() is tearing down shp */
+		if (shm_file == NULL) {
+			err = -EIDRM;
+			goto out_unlock0;
+		}
+
 		if (is_file_hugepages(shm_file))
 			goto out_unlock0;
 
@@ -1101,6 +1114,14 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
 		goto out_unlock;
 
 	ipc_lock_object(&shp->shm_perm);
+
+	/* check if shm_destroy() is tearing down shp */
+	if (shp->shm_file == NULL) {
+		ipc_unlock_object(&shp->shm_perm);
+		err = -EIDRM;
+		goto out_unlock;
+	}
+
 	path = shp->shm_file->f_path;
 	path_get(&path);
 	shp->shm_nattch++;