[PATCH v2 19/23] xfs: fix memory leak in xfs_dqinode_metadir_create()

[Andrey Albershteyn <aalbersh@kernel.org>]

From: Dawei Feng <dawei.feng@seu.edu.cn>

Source kernel commit: 45de375b25060edf46e20abb36521ba530336ceb

If xfs_metadir_create() fails in xfs_dqinode_metadir_create(), the current
code returns directly, leaking the allocated update and transaction state.
If the subsequent commit fails, the caller-owned inode reference is left
behind.

Fix this memory leak by routing the create failure path through
xfs_metadir_cancel().  For both create and commit failures, finish and
release any inode returned to the caller, mirroring the unwind pattern in
xfs_metadir_mkdir().

The bug was first flagged by an experimental analysis tool we are
developing for kernel memory-management bugs while analyzing
v6.13-rc1. The tool is still under development and is not yet publicly
available. Manual inspection confirms that the bug is still
present in v7.1.1.

An x86_64 allyesconfig build showed no new warnings. Runtime validation
used kprobe fault injection during `mount -o uquota` on a metadir XFS
image. Injecting xfs_metadir_create() reproduced the old active-update path
that left mount stuck later in mount setup; after this change, the same
injection reported cancel_hits=1 and irele_hits=1. Injecting
xfs_metadir_commit() exercised the old inode-reference leak path; after
this change, it reported irele_hits=1.

Fixes: e80fbe1ad8ef ("xfs: use metadir for quota inodes")
Signed-off-by: Dawei Feng <dawei.feng@seu.edu.cn>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
---
 libxfs/xfs_dquot_buf.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/libxfs/xfs_dquot_buf.c b/libxfs/xfs_dquot_buf.c
index 329aceca005d..5022073e0c4a 100644
--- a/libxfs/xfs_dquot_buf.c
+++ b/libxfs/xfs_dquot_buf.c
@@ -434,17 +434,27 @@ xfs_dqinode_metadir_create(
 
 	error = xfs_metadir_create(&upd, S_IFREG);
 	if (error)
-		return error;
+		goto out_cancel;
 
 	xfs_trans_log_inode(upd.tp, upd.ip, XFS_ILOG_CORE);
 
 	error = xfs_metadir_commit(&upd);
 	if (error)
-		return error;
+		goto out_irele;
 
 	xfs_finish_inode_setup(upd.ip);
 	*ipp = upd.ip;
 	return 0;
+
+out_cancel:
+	xfs_metadir_cancel(&upd, error);
+out_irele:
+	/* Have to finish setting up the inode to ensure it's deleted. */
+	if (upd.ip) {
+		xfs_finish_inode_setup(upd.ip);
+		xfs_irele(upd.ip);
+	}
+	return error;
 }
 
 #ifndef __KERNEL__
-- 
2.55.0