ipc,shm: shorten critical region for shmctl
Davidlohr Bueso [Wed, 11 Sep 2013 21:26:21 +0000 (14:26 -0700)]
commit 2caacaa82a51b78fc0c800e206473874094287ed upstream.

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>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

ipc/shm.c

index 8fd9ab3..a204d0b 100644 (file)
--- 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;
 }