[XFS] Really fix use after free in xfs_iunpin.

The previous attempts to fix the linux inode use-after-free in xfs_iunpin
simply made the problem harder to hit. We actually need complete exclusion
between xfs_reclaim and xfs_iunpin, as well as ensuring that the i_flags
are consistent during both of these functions. Introduce a new spinlock
for exclusion and the i_flags, and fix up xfs_iunpin to use igrab before
marking the inode dirty.

SGI-PV: 952967
SGI-Modid: xfs-linux-melb:xfs-kern:26964a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

6 files changed, 35 insertions, 3 deletions

diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index 9df9ed37d219..38c4d128a8c0 100644
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -227,7 +227,9 @@ xfs_initialize_vnode(
                 xfs_revalidate_inode(XFS_BHVTOM(bdp), vp, ip);
                 xfs_set_inodeops(inode);
 
+                spin_lock(&ip->i_flags_lock);
                 ip->i_flags &= ~XFS_INEW;
+                spin_unlock(&ip->i_flags_lock);
                 barrier();
 
                 unlock_new_inode(inode);
diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index 9b9379792f37..b73d216ecaf9 100644
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -243,7 +243,9 @@ again:
 
                                 XFS_STATS_INC(xs_ig_found);
 
+                                spin_lock(&ip->i_flags_lock);
                                 ip->i_flags &= ~XFS_IRECLAIMABLE;
+                                spin_unlock(&ip->i_flags_lock);
                                 version = ih->ih_version;
                                 read_unlock(&ih->ih_lock);
                                 xfs_ihash_promote(ih, ip, version);
@@ -297,7 +299,9 @@ finish_inode:
                         if (lock_flags != 0)
                                 xfs_ilock(ip, lock_flags);
 
+                        spin_lock(&ip->i_flags_lock);
                         ip->i_flags &= ~XFS_ISTALE;
+                        spin_unlock(&ip->i_flags_lock);
 
                         vn_trace_exit(vp, "xfs_iget.found",
                                                 (inst_t *)__return_address);
@@ -367,7 +371,9 @@ finish_inode:
         ih->ih_next = ip;
         ip->i_udquot = ip->i_gdquot = NULL;
         ih->ih_version++;
+        spin_lock(&ip->i_flags_lock);
         ip->i_flags |= XFS_INEW;
+        spin_unlock(&ip->i_flags_lock);
 
         write_unlock(&ih->ih_lock);
 
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 66a78287a957..c27d7d495aa0 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -867,6 +867,7 @@ xfs_iread(
         ip = kmem_zone_zalloc(xfs_inode_zone, KM_SLEEP);
         ip->i_ino = ino;
         ip->i_mount = mp;
+        spin_lock_init(&ip->i_flags_lock);
 
         /*
          * Get pointer's to the on-disk inode and the buffer containing it.
@@ -2214,7 +2215,9 @@ xfs_ifree_cluster(
 
                         if (ip == free_ip) {
                                 if (xfs_iflock_nowait(ip)) {
+                                        spin_lock(&ip->i_flags_lock);
                                         ip->i_flags |= XFS_ISTALE;
+                                        spin_unlock(&ip->i_flags_lock);
 
                                         if (xfs_inode_clean(ip)) {
                                                 xfs_ifunlock(ip);
@@ -2228,7 +2231,9 @@ xfs_ifree_cluster(
 
                         if (xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
                                 if (xfs_iflock_nowait(ip)) {
+                                        spin_lock(&ip->i_flags_lock);
                                         ip->i_flags |= XFS_ISTALE;
+                                        spin_unlock(&ip->i_flags_lock);
 
                                         if (xfs_inode_clean(ip)) {
                                                 xfs_ifunlock(ip);
@@ -2258,7 +2263,9 @@ xfs_ifree_cluster(
                                 AIL_LOCK(mp,s);
                                 iip->ili_flush_lsn = iip->ili_item.li_lsn;
                                 AIL_UNLOCK(mp, s);
+                                spin_lock(&iip->ili_inode->i_flags_lock);
                                 iip->ili_inode->i_flags |= XFS_ISTALE;
+                                spin_unlock(&iip->ili_inode->i_flags_lock);
                                 pre_flushed++;
                         }
                         lip = lip->li_bio_list;
@@ -2754,19 +2761,29 @@ xfs_iunpin(
                  * call as the inode reclaim may be blocked waiting for
                  * the inode to become unpinned.
                  */
+                struct inode *inode = NULL;
+
+                spin_lock(&ip->i_flags_lock);
                 if (!(ip->i_flags & (XFS_IRECLAIM|XFS_IRECLAIMABLE))) {
                         bhv_vnode_t     *vp = XFS_ITOV_NULL(ip);
 
                         /* make sync come back and flush this inode */
                         if (vp) {
-                                struct inode    *inode = vn_to_inode(vp);
+                                inode = vn_to_inode(vp);
 
                                 if (!(inode->i_state &
-                                                (I_NEW|I_FREEING|I_CLEAR)))
-                                        mark_inode_dirty_sync(inode);
+                                                (I_NEW|I_FREEING|I_CLEAR))) {
+                                        inode = igrab(inode);
+                                        if (inode)
+                                                mark_inode_dirty_sync(inode);
+                                } else
+                                        inode = NULL;
                         }
                 }
+                spin_unlock(&ip->i_flags_lock);
                 wake_up(&ip->i_ipin_wait);
+                if (inode)
+                        iput(inode);
         }
 }
 
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index fdb89f72db95..e96eb0835fe6 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -267,6 +267,7 @@ typedef struct xfs_inode {
         sema_t                  i_flock;        /* inode flush lock */
         atomic_t                i_pincount;     /* inode pin count */
         wait_queue_head_t       i_ipin_wait;    /* inode pinning wait queue */
+        spinlock_t              i_flags_lock;   /* inode i_flags lock */
 #ifdef HAVE_REFCACHE
         struct xfs_inode        **i_refcache;   /* ptr to entry in ref cache */
         struct xfs_inode        *i_release;     /* inode to unref */
diff --git a/fs/xfs/xfs_itable.c b/fs/xfs/xfs_itable.c
index b608b8ab1dd6..136c6b06f1c9 100644
--- a/fs/xfs/xfs_itable.c
+++ b/fs/xfs/xfs_itable.c
@@ -577,6 +577,7 @@ xfs_bulkstat(
                                                                       KM_SLEEP);
                                                 ip->i_ino = ino;
                                                 ip->i_mount = mp;
+                                                spin_lock_init(&ip->i_flags_lock);
                                                 if (bp)
                                                         xfs_buf_relse(bp);
                                                 error = xfs_itobp(mp, NULL, ip,
diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 1a6782eaf5d4..061e2ffdd1de 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -3844,7 +3844,9 @@ xfs_reclaim(
                 XFS_MOUNT_ILOCK(mp);
                 vn_bhv_remove(VN_BHV_HEAD(vp), XFS_ITOBHV(ip));
                 list_add_tail(&ip->i_reclaim, &mp->m_del_inodes);
+                spin_lock(&ip->i_flags_lock);
                 ip->i_flags |= XFS_IRECLAIMABLE;
+                spin_unlock(&ip->i_flags_lock);
                 XFS_MOUNT_IUNLOCK(mp);
         }
         return 0;
@@ -3869,8 +3871,10 @@ xfs_finish_reclaim(
          * us.
          */
         write_lock(&ih->ih_lock);
+        spin_lock(&ip->i_flags_lock);
         if ((ip->i_flags & XFS_IRECLAIM) ||
             (!(ip->i_flags & XFS_IRECLAIMABLE) && vp == NULL)) {
+                spin_unlock(&ip->i_flags_lock);
                 write_unlock(&ih->ih_lock);
                 if (locked) {
                         xfs_ifunlock(ip);
@@ -3879,6 +3883,7 @@ xfs_finish_reclaim(
                 return 1;
         }
         ip->i_flags |= XFS_IRECLAIM;
+        spin_unlock(&ip->i_flags_lock);
         write_unlock(&ih->ih_lock);
 
         /*