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 and move an ASSERT in xfs_buf_rele() so that we can catch more cases.

@@ -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);
}

+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)

Looks good, but please mark xfs_buf_item_free static.