[06/38] xfs: use an empty transaction to protect xfs_attr_get from deadlocks

Commit Message

Darrick J. Wong April 30, 2024, 3:32 a.m. UTC

From: Darrick J. Wong <[e-mail]>

Wrap the xfs_attr_get_ilocked call in xfs_attr_get with an empty
transaction so that we cannot livelock the kernel if someone injects a
loop into the attr structure or the attr fork bmbt.

Signed-off-by: Darrick J. Wong <[e-mail]>
---
 libxfs/xfs_attr.c |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

Patch

diff --git a/libxfs/xfs_attr.c b/libxfs/xfs_attr.c
index 3058e609c514..0a9fb396885e 100644
--- a/libxfs/xfs_attr.c
+++ b/libxfs/xfs_attr.c
@@ -273,6 +273,8 @@  xfs_attr_get(
 
 	XFS_STATS_INC(args->dp->i_mount, xs_attr_get);
 
+	ASSERT(!args->trans);
+
 	if (xfs_is_shutdown(args->dp->i_mount))
 		return -EIO;
 
@@ -285,8 +287,27 @@  xfs_attr_get(
 	/* Entirely possible to look up a name which doesn't exist */
 	args->op_flags = XFS_DA_OP_OKNOENT;
 
+	error = xfs_trans_alloc_empty(args->dp->i_mount, &args->trans);
+	if (error)
+		return error;
+
 	lock_mode = xfs_ilock_attr_map_shared(args->dp);
+
+        /*
+	 * Make sure the attr fork iext tree is loaded.  Use the empty
+	 * transaction to load the bmbt so that we avoid livelocking on loops.
+	 */
+        if (xfs_inode_hasattr(args->dp)) {
+                error = xfs_iread_extents(args->trans, args->dp, XFS_ATTR_FORK);
+                if (error)
+                        goto out_cancel;
+        }
+
 	error = xfs_attr_get_ilocked(args);
+
+out_cancel:
+	xfs_trans_cancel(args->trans);
+	args->trans = NULL;
 	xfs_iunlock(args->dp, lock_mode);
 
 	return error;