[XFS] Fix use-after-free with buffers

We have a use-after-free issue where log completions access buffers via
the buffer log item and the buffer has already been freed. Fix this by
taking a reference on the buffer when attaching the buffer log item and
release the hold when the buffer log item is detached and we no longer
need the buffer. Also create a new function xfs_buf_item_free() to combine
some common code.

SGI-PV: 985757

SGI-Modid: xfs-linux-melb:xfs-kern:32025a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>

1 files changed, 20 insertions, 24 deletions

diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 608c30c3f76b..002fc2617c8e 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -732,6 +732,7 @@ xfs_buf_item_init(
         bip->bli_item.li_ops = &xfs_buf_item_ops;
         bip->bli_item.li_mountp = mp;
         bip->bli_buf = bp;
+        xfs_buf_hold(bp);
         bip->bli_format.blf_type = XFS_LI_BUF;
         bip->bli_format.blf_blkno = (__int64_t)XFS_BUF_ADDR(bp);
         bip->bli_format.blf_len = (ushort)BTOBB(XFS_BUF_COUNT(bp));
@@ -867,6 +868,21 @@ xfs_buf_item_dirty(
         return (bip->bli_flags & XFS_BLI_DIRTY);
 }
 
+STATIC void
+xfs_buf_item_free(
+        xfs_buf_log_item_t      *bip)
+{
+#ifdef XFS_TRANS_DEBUG
+        kmem_free(bip->bli_orig);
+        kmem_free(bip->bli_logged);
+#endif /* XFS_TRANS_DEBUG */
+
+#ifdef XFS_BLI_TRACE
+        ktrace_free(bip->bli_trace);
+#endif
+        kmem_zone_free(xfs_buf_item_zone, bip);
+}
+
 /*
  * This is called when the buf log item is no longer needed.  It should
  * free the buf log item associated with the given buffer and clear
@@ -887,18 +903,8 @@ xfs_buf_item_relse(
             (XFS_BUF_IODONE_FUNC(bp) != NULL)) {
                 XFS_BUF_CLR_IODONE_FUNC(bp);
         }
-
-#ifdef XFS_TRANS_DEBUG
-        kmem_free(bip->bli_orig);
-        bip->bli_orig = NULL;
-        kmem_free(bip->bli_logged);
-        bip->bli_logged = NULL;
-#endif /* XFS_TRANS_DEBUG */
-
-#ifdef XFS_BLI_TRACE
-        ktrace_free(bip->bli_trace);
-#endif
-        kmem_zone_free(xfs_buf_item_zone, bip);
+        xfs_buf_rele(bp);
+        xfs_buf_item_free(bip);
 }
 
 
@@ -1120,6 +1126,7 @@ xfs_buf_iodone(
 
         ASSERT(bip->bli_buf == bp);
 
+        xfs_buf_rele(bp);
         mp = bip->bli_item.li_mountp;
 
         /*
@@ -1136,18 +1143,7 @@ xfs_buf_iodone(
          * xfs_trans_delete_ail() drops the AIL lock.
          */
         xfs_trans_delete_ail(mp, (xfs_log_item_t *)bip);
-
-#ifdef XFS_TRANS_DEBUG
-        kmem_free(bip->bli_orig);
-        bip->bli_orig = NULL;
-        kmem_free(bip->bli_logged);
-        bip->bli_logged = NULL;
-#endif /* XFS_TRANS_DEBUG */
-
-#ifdef XFS_BLI_TRACE
-        ktrace_free(bip->bli_trace);
-#endif
-        kmem_zone_free(xfs_buf_item_zone, bip);
+        xfs_buf_item_free(bip);
 }
 
 #if defined(XFS_BLI_TRACE)