[09/24] xfs: use an empty transaction to protect xfs_attr_get from deadlocks

Commit Message

Andrey Albershteyn Dec. 29, 2024, 1:39 p.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]>
---
 fs/xfs/libxfs/xfs_attr.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Patch

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index e452ca55241f..3f3699e9c203 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -274,6 +274,8 @@  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;
 
@@ -286,8 +288,14 @@  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);
 	error = xfs_attr_get_ilocked(args);
+	xfs_trans_cancel(args->trans);
+	args->trans = NULL;
 	xfs_iunlock(args->dp, lock_mode);
 
 	return error;