releases/3.11.6/ipc-shm-make-shmctl_nolock-lockless.patch

   1 From c97cb9ccab8c85428ec21eff690642ad2ce1fa8a Mon Sep 17 00:00:00 2001
   2 From: Davidlohr Bueso <davidlohr.bueso@hp.com>
   3 Date: Wed, 11 Sep 2013 14:26:20 -0700
   4 Subject: ipc,shm: make shmctl_nolock lockless
   5
   6 From: Davidlohr Bueso <davidlohr.bueso@hp.com>
   7
   8 commit c97cb9ccab8c85428ec21eff690642ad2ce1fa8a upstream.
   9
  10 While the INFO cmd doesn't take the ipc lock, the STAT commands do acquire
  11 it unnecessarily.  We can do the permissions and security checks only
  12 holding the rcu lock.
  13
  14 [akpm@linux-foundation.org: coding-style fixes]
  15 Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
  16 Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
  17 Cc: Rik van Riel <riel@redhat.com>
  18 Cc: Manfred Spraul <manfred@colorfullife.com>
  19 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  20 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  21 Cc: Mike Galbraith <efault@gmx.de>
  22 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  23
  24 ---
  25  ipc/shm.c |   19 ++++++++++++-------
  26  1 file changed, 12 insertions(+), 7 deletions(-)
  27
  28 --- a/ipc/shm.c
  29 +++ b/ipc/shm.c
  30 @@ -889,27 +889,31 @@ static int shmctl_nolock(struct ipc_name
  31                 struct shmid64_ds tbuf;
  32                 int result;
  33
  34 +               rcu_read_lock();
  35                 if (cmd == SHM_STAT) {
  36 -                       shp = shm_lock(ns, shmid);
  37 +                       shp = shm_obtain_object(ns, shmid);
  38                         if (IS_ERR(shp)) {
  39                                 err = PTR_ERR(shp);
  40 -                               goto out;
  41 +                               goto out_unlock;
  42                         }
  43                         result = shp->shm_perm.id;
  44                 } else {
  45 -                       shp = shm_lock_check(ns, shmid);
  46 +                       shp = shm_obtain_object_check(ns, shmid);
  47                         if (IS_ERR(shp)) {
  48                                 err = PTR_ERR(shp);
  49 -                               goto out;
  50 +                               goto out_unlock;
  51                         }
  52                         result = 0;
  53                 }
  54 +
  55                 err = -EACCES;
  56                 if (ipcperms(ns, &shp->shm_perm, S_IRUGO))
  57                         goto out_unlock;
  58 +
  59                 err = security_shm_shmctl(shp, cmd);
  60                 if (err)
  61                         goto out_unlock;
  62 +
  63                 memset(&tbuf, 0, sizeof(tbuf));
  64                 kernel_to_ipc64_perm(&shp->shm_perm, &tbuf.shm_perm);
  65                 tbuf.shm_segsz  = shp->shm_segsz;
  66 @@ -919,8 +923,9 @@ static int shmctl_nolock(struct ipc_name
  67                 tbuf.shm_cpid   = shp->shm_cprid;
  68                 tbuf.shm_lpid   = shp->shm_lprid;
  69                 tbuf.shm_nattch = shp->shm_nattch;
  70 -               shm_unlock(shp);
  71 -               if(copy_shmid_to_user (buf, &tbuf, version))
  72 +               rcu_read_unlock();
  73 +
  74 +               if (copy_shmid_to_user(buf, &tbuf, version))
  75                         err = -EFAULT;
  76                 else
  77                         err = result;
  78 @@ -931,7 +936,7 @@ static int shmctl_nolock(struct ipc_name
  79         }
  80
  81  out_unlock:
  82 -       shm_unlock(shp);
  83 +       rcu_read_unlock();
  84  out:
  85         return err;
  86  }