xfs: fix stale inode flush avoidance

When reclaiming stale inodes, we need to guarantee that inodes are
unpinned before returning with a "clean" status. If we don't we can
reclaim inodes that are pinned, leading to use after free in the
transaction subsystem as transactions complete.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 15 insertions, 6 deletions

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 391d36b0e68c..ef77fd88c8e3 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2842,13 +2842,9 @@ xfs_iflush(
 
         /*
          * If the inode isn't dirty, then just release the inode flush lock and
-         * do nothing. Treat stale inodes the same; we cannot rely on the
-         * backing buffer remaining stale in cache for the remaining life of
-         * the stale inode and so xfs_itobp() below may give us a buffer that
-         * no longer contains inodes below. Doing this stale check here also
-         * avoids forcing the log on pinned, stale inodes.
+         * do nothing.
          */
-        if (xfs_inode_clean(ip) || xfs_iflags_test(ip, XFS_ISTALE)) {
+        if (xfs_inode_clean(ip)) {
                 xfs_ifunlock(ip);
                 return 0;
         }
@@ -2872,6 +2868,19 @@ xfs_iflush(
         xfs_iunpin_wait(ip);
 
         /*
+         * For stale inodes we cannot rely on the backing buffer remaining
+         * stale in cache for the remaining life of the stale inode and so
+         * xfs_itobp() below may give us a buffer that no longer contains
+         * inodes below. We have to check this after ensuring the inode is
+         * unpinned so that it is safe to reclaim the stale inode after the
+         * flush call.
+         */
+        if (xfs_iflags_test(ip, XFS_ISTALE)) {
+                xfs_ifunlock(ip);
+                return 0;
+        }
+
+        /*
          * This may have been unpinned because the filesystem is shutting
          * down forcibly. If that's the case we must not write this inode
          * to disk, because the log record didn't make it to disk!