ipc,shm: shorten critical region for shmctl

With the *_INFO, *_STAT, IPC_RMID and IPC_SET commands already optimized,
deal with the remaining SHM_LOCK and SHM_UNLOCK commands.  Take the
shm_perm lock after doing the initial auditing and security checks.  The
rest of the logic remains unchanged.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
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, 25 insertions, 24 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index a493639550d9..8ec381085dec 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -940,10 +940,8 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
         int err, version;
         struct ipc_namespace *ns;
 
-        if (cmd < 0 || shmid < 0) {
-                err = -EINVAL;
-                goto out;
-        }
+        if (cmd < 0 || shmid < 0)
+                return -EINVAL;
 
         version = ipc_parse_version(&cmd);
         ns = current->nsproxy->ipc_ns;
@@ -954,36 +952,40 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
         case SHM_STAT:
         case IPC_STAT:
                 return shmctl_nolock(ns, shmid, cmd, version, buf);
+        case IPC_RMID:
+        case IPC_SET:
+                return shmctl_down(ns, shmid, cmd, buf, version);
         case SHM_LOCK:
         case SHM_UNLOCK:
         {
                 struct file *shm_file;
 
-                shp = shm_lock_check(ns, shmid);
+                rcu_read_lock();
+                shp = shm_obtain_object_check(ns, shmid);
                 if (IS_ERR(shp)) {
                         err = PTR_ERR(shp);
-                        goto out;
+                        goto out_unlock1;
                 }
 
                 audit_ipc_obj(&(shp->shm_perm));
+                err = security_shm_shmctl(shp, cmd);
+                if (err)
+                        goto out_unlock1;
 
+                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))
-                                goto out_unlock;
+                                goto out_unlock0;
                         if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
-                                goto out_unlock;
+                                goto out_unlock0;
                 }
 
-                err = security_shm_shmctl(shp, cmd);
-                if (err)
-                        goto out_unlock;
-
                 shm_file = shp->shm_file;
                 if (is_file_hugepages(shm_file))
-                        goto out_unlock;
+                        goto out_unlock0;
 
                 if (cmd == SHM_LOCK) {
                         struct user_struct *user = current_user();
@@ -992,32 +994,31 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
                                 shp->shm_perm.mode |= SHM_LOCKED;
                                 shp->mlock_user = user;
                         }
-                        goto out_unlock;
+                        goto out_unlock0;
                 }
 
                 /* SHM_UNLOCK */
                 if (!(shp->shm_perm.mode & SHM_LOCKED))
-                        goto out_unlock;
+                        goto out_unlock0;
                 shmem_lock(shm_file, 0, shp->mlock_user);
                 shp->shm_perm.mode &= ~SHM_LOCKED;
                 shp->mlock_user = NULL;
                 get_file(shm_file);
-                shm_unlock(shp);
+                ipc_unlock_object(&shp->shm_perm);
+                rcu_read_unlock();
                 shmem_unlock_mapping(shm_file->f_mapping);
+
                 fput(shm_file);
-                goto out;
-        }
-        case IPC_RMID:
-        case IPC_SET:
-                err = shmctl_down(ns, shmid, cmd, buf, version);
                 return err;
+        }
         default:
                 return -EINVAL;
         }
 
-out_unlock:
-        shm_unlock(shp);
-out:
+out_unlock0:
+        ipc_unlock_object(&shp->shm_perm);
+out_unlock1:
+        rcu_read_unlock();
         return err;
 }