xfs: fix an incore inode UAF in xfs_bui_recoverfix-log-recovery_2020-06-01

In xfs_bui_item_recover, there exists a use-after-free bug with regards
to the inode that is involved in the bmap replay operation.  If the
mapping operation does not complete, we call xfs_bmap_unmap_extent to
create a deferred op to finish the unmapping work, and we retain a
pointer to the incore inode.

Unfortunately, the very next thing we do is commit the transaction and
drop the inode.  If reclaim tears down the inode before we try to finish
the defer ops, we dereference garbage and blow up.  Therefore, create a
way to join inodes to the defer ops freezer so that we can maintain the
xfs_inode reference until we're done with the inode.

Note: This imposes the requirement that there be enough memory to keep
every incore inode in memory throughout recovery.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

4 files changed, 102 insertions, 0 deletions

diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
index 043f516ff940..e23fc065d6e0 100644
--- a/fs/xfs/libxfs/xfs_defer.c
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -16,6 +16,7 @@
 #include "xfs_inode.h"
 #include "xfs_inode_item.h"
 #include "xfs_trace.h"
+#include "xfs_icache.h"
 
 /*
  * Deferred Operations in XFS
@@ -595,6 +596,8 @@ xfs_defer_continue(
 	ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
 	ASSERT(!(tp->t_flags & XFS_TRANS_DIRTY));
 
+	xfs_defer_continue_inodes(dfc, tp);
+
 	/* Move captured dfops chain and state to the transaction. */
 	list_splice_init(&dfc->dfc_dfops, &tp->t_dfops);
 	tp->t_flags |= dfc->dfc_tpflags;
@@ -610,5 +613,42 @@ xfs_defer_capture_free(
 	struct xfs_defer_capture	*dfc)
 {
 	xfs_defer_cancel_list(mp, &dfc->dfc_dfops);
+	xfs_defer_capture_irele(dfc);
 	kmem_free(dfc);
 }
+
+/*
+ * Capture an inode along with the deferred ops freezer.  Callers must hold
+ * ILOCK_EXCL, which will be dropped and reacquired when we're ready to
+ * continue replaying the deferred ops.
+ */
+int
+xfs_defer_capture_inode(
+	struct xfs_defer_capture	*dfc,
+	struct xfs_inode		*ip)
+{
+	unsigned int			i;
+
+	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
+
+	for (i = 0; i < XFS_DEFER_CAPTURE_INODES; i++) {
+		if (dfc->dfc_inodes[i] == ip)
+			goto out;
+		if (dfc->dfc_inodes[i] == NULL)
+			break;
+	}
+
+	if (i == XFS_DEFER_CAPTURE_INODES) {
+		ASSERT(0);
+		return -EFSCORRUPTED;
+	}
+
+	/*
+	 * Attach this inode to the freezer and drop its ILOCK because we
+	 * assume the caller will need to allocate a transaction.
+	 */
+	dfc->dfc_inodes[i] = ip;
+out:
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return 0;
+}
diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
index a0ad379e38f8..532439dc5ec9 100644
--- a/fs/xfs/libxfs/xfs_defer.h
+++ b/fs/xfs/libxfs/xfs_defer.h
@@ -77,6 +77,11 @@ struct xfs_defer_capture {
 	struct list_head	dfc_dfops;
 	unsigned int		dfc_tpflags;
 	unsigned int		dfc_blkres;
+
+	/* Inodes to hold when we want to finish the deferred work items. */
+	unsigned int		dfc_ilockflags;
+#define XFS_DEFER_CAPTURE_INODES	2
+	struct xfs_inode	*dfc_inodes[XFS_DEFER_CAPTURE_INODES];
 };
 
 /*
@@ -87,5 +92,12 @@ int xfs_defer_capture(struct xfs_trans *tp, struct xfs_defer_capture **dfcp);
 void xfs_defer_continue(struct xfs_defer_capture *dfc, struct xfs_trans *tp);
 void xfs_defer_capture_free(struct xfs_mount *mp,
 		struct xfs_defer_capture *dfc);
+int xfs_defer_capture_inode(struct xfs_defer_capture *dfc,
+		struct xfs_inode *ip);
+
+/* These functions must be provided by the xfs implementation. */
+void xfs_defer_continue_inodes(struct xfs_defer_capture *dfc,
+		struct xfs_trans *tp);
+void xfs_defer_capture_irele(struct xfs_defer_capture *dfc);
 
 #endif /* __XFS_DEFER_H__ */
diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
index d1b5554ac457..b901d953cfb8 100644
--- a/fs/xfs/xfs_bmap_item.c
+++ b/fs/xfs/xfs_bmap_item.c
@@ -510,6 +510,9 @@ xfs_bui_item_recover(
 
 	/* Commit transaction, which frees tp. */
 	error = xlog_recover_trans_commit(tp, dfcp);
+	if (error || count == 0)
+		goto err_unlock;
+	error = xfs_defer_capture_inode(*dfcp, ip);
 	if (error)
 		goto err_unlock;
 	return 0;
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 78cda96b621f..d87c974e9b6f 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -12,6 +12,7 @@
 #include "xfs_sb.h"
 #include "xfs_mount.h"
 #include "xfs_inode.h"
+#include "xfs_defer.h"
 #include "xfs_trans.h"
 #include "xfs_trans_priv.h"
 #include "xfs_inode_item.h"
@@ -2430,3 +2431,49 @@ xfs_inactive_force_poll(
 		touch_softlockup_watchdog();
 	}
 }
+
+/* Re-acquire the inode locks and attach them to the transaction. */
+void
+xfs_defer_continue_inodes(
+	struct xfs_defer_capture	*dfc,
+	struct xfs_trans		*tp)
+{
+	int				i;
+	int				error;
+
+	for (i = 0; i < XFS_DEFER_CAPTURE_INODES && dfc->dfc_inodes[i]; i++) {
+		error = xfs_qm_dqattach(dfc->dfc_inodes[i]);
+		if (error)
+			tp->t_mountp->m_qflags &= ~XFS_ALL_QUOTA_CHKD;
+	}
+
+	dfc->dfc_ilockflags = XFS_ILOCK_EXCL;
+	if (dfc->dfc_inodes[1]) {
+		xfs_lock_two_inodes(dfc->dfc_inodes[0], dfc->dfc_ilockflags,
+				    dfc->dfc_inodes[1], dfc->dfc_ilockflags);
+		xfs_trans_ijoin(tp, dfc->dfc_inodes[0], 0);
+		xfs_trans_ijoin(tp, dfc->dfc_inodes[1], 0);
+	} else if (dfc->dfc_inodes[0]) {
+		xfs_ilock(dfc->dfc_inodes[0], dfc->dfc_ilockflags);
+		xfs_trans_ijoin(tp, dfc->dfc_inodes[0], 0);
+	}
+}
+
+/* Release all the inode resources attached to this dfops capture device. */
+void
+xfs_defer_capture_irele(
+	struct xfs_defer_capture	*dfc)
+{
+	unsigned int			i;
+
+	for (i = 0; i < XFS_DEFER_CAPTURE_INODES; i++) {
+		if (!dfc->dfc_inodes[i])
+			break;
+
+		if (dfc->dfc_ilockflags)
+			xfs_iunlock(dfc->dfc_inodes[i], dfc->dfc_ilockflags);
+		xfs_irele(dfc->dfc_inodes[i]);
+		dfc->dfc_inodes[i] = NULL;
+	}
+	dfc->dfc_ilockflags = 0;
+}