From 6ae13c0feb96a1ea97e814213271b41b3d090d2d Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 7 Aug 2021 23:18:26 +0300
Subject: [PATCH] msdosfs: add doscheckpath lock

Similar to the UFS revision 8df4bc48c89a130207

Reviewed by:	mckusick
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D31464
---
 sys/fs/msdosfs/msdosfs_lookup.c |  1 +
 sys/fs/msdosfs/msdosfs_vfsops.c |  3 +++
 sys/fs/msdosfs/msdosfs_vnops.c  | 11 ++++++++++-
 sys/fs/msdosfs/msdosfsmount.h   |  1 +
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/sys/fs/msdosfs/msdosfs_lookup.c b/sys/fs/msdosfs/msdosfs_lookup.c
index 2c3d02db37a0..9940800a72c2 100644
--- a/sys/fs/msdosfs/msdosfs_lookup.c
+++ b/sys/fs/msdosfs/msdosfs_lookup.c
@@ -813,6 +813,7 @@ doscheckpath(struct denode *source, struct denode *target, daddr_t *wait_scn)
 	*wait_scn = 0;
 
 	pmp = target->de_pmp;
+	lockmgr_assert(&pmp->pm_checkpath_lock, KA_XLOCKED);
 	KASSERT(pmp == source->de_pmp,
 	    ("doscheckpath: source and target on different filesystems"));
 
diff --git a/sys/fs/msdosfs/msdosfs_vfsops.c b/sys/fs/msdosfs/msdosfs_vfsops.c
index 68c8a93a18af..0f6d41b3c77c 100644
--- a/sys/fs/msdosfs/msdosfs_vfsops.c
+++ b/sys/fs/msdosfs/msdosfs_vfsops.c
@@ -469,6 +469,7 @@ mountmsdosfs(struct vnode *devvp, struct mount *mp)
 	pmp->pm_bo = bo;
 
 	lockinit(&pmp->pm_fatlock, 0, msdosfs_lock_msg, 0, 0);
+	lockinit(&pmp->pm_checkpath_lock, 0, "msdoscp", 0, 0);
 
 	/*
 	 * Initialize ownerships and permissions, since nothing else will
@@ -740,6 +741,7 @@ mountmsdosfs(struct vnode *devvp, struct mount *mp)
 	}
 	if (pmp) {
 		lockdestroy(&pmp->pm_fatlock);
+		lockdestroy(&pmp->pm_checkpath_lock);
 		free(pmp->pm_inusemap, M_MSDOSFSFAT);
 		free(pmp, M_MSDOSFSMNT);
 		mp->mnt_data = NULL;
@@ -829,6 +831,7 @@ msdosfs_unmount(struct mount *mp, int mntflags)
 	dev_rel(pmp->pm_dev);
 	free(pmp->pm_inusemap, M_MSDOSFSFAT);
 	lockdestroy(&pmp->pm_fatlock);
+	lockdestroy(&pmp->pm_checkpath_lock);
 	free(pmp, M_MSDOSFSMNT);
 	mp->mnt_data = NULL;
 	MNT_ILOCK(mp);
diff --git a/sys/fs/msdosfs/msdosfs_vnops.c b/sys/fs/msdosfs/msdosfs_vnops.c
index c81e192a6158..6197340e8943 100644
--- a/sys/fs/msdosfs/msdosfs_vnops.c
+++ b/sys/fs/msdosfs/msdosfs_vnops.c
@@ -942,7 +942,7 @@ msdosfs_rename(struct vop_rename_args *ap)
 	struct denode *fdip, *fip, *tdip, *tip, *nip;
 	u_char toname[12], oldname[11];
 	u_long from_diroffset, to_diroffset;
-	bool doingdirectory, newparent;
+	bool checkpath_locked, doingdirectory, newparent;
 	u_char to_count;
 	int error;
 	u_long cn, pcl, blkoff;
@@ -991,6 +991,8 @@ msdosfs_rename(struct vop_rename_args *ap)
 	if (tvp != NULL && tvp != tdvp)
 		VOP_UNLOCK(tvp);
 
+	checkpath_locked = false;
+
 relock:
 	doingdirectory = newparent = false;
 
@@ -1113,8 +1115,12 @@ msdosfs_rename(struct vop_rename_args *ap)
 	if (doingdirectory && newparent) {
 		if (error != 0)	/* write access check above */
 			goto unlock;
+		lockmgr(&pmp->pm_checkpath_lock, LK_EXCLUSIVE, NULL);
+		checkpath_locked = true;
 		error = doscheckpath(fip, tdip, &wait_scn);
 		if (wait_scn != 0) {
+			lockmgr(&pmp->pm_checkpath_lock, LK_RELEASE, NULL);
+			checkpath_locked = false;
 			VOP_UNLOCK(fdvp);
 			VOP_UNLOCK(tdvp);
 			VOP_UNLOCK(fvp);
@@ -1268,6 +1274,8 @@ msdosfs_rename(struct vop_rename_args *ap)
 	cache_purge(fvp);
 
 unlock:
+	if (checkpath_locked)
+		lockmgr(&pmp->pm_checkpath_lock, LK_RELEASE, NULL);
 	vput(fdvp);
 	vput(fvp);
 	if (tvp != NULL) {
@@ -1279,6 +1287,7 @@ msdosfs_rename(struct vop_rename_args *ap)
 	vput(tdvp);
 	return (error);
 releout:
+	MPASS(!checkpath_locked);
 	vrele(tdvp);
 	if (tvp != NULL)
 		vrele(tvp);
diff --git a/sys/fs/msdosfs/msdosfsmount.h b/sys/fs/msdosfs/msdosfsmount.h
index 75b187860270..46a02e611cf5 100644
--- a/sys/fs/msdosfs/msdosfsmount.h
+++ b/sys/fs/msdosfs/msdosfsmount.h
@@ -114,6 +114,7 @@ struct msdosfsmount {
 	void *pm_d2u;	/* DOS->Local iconv handle */
 #ifndef MAKEFS
 	struct lock pm_fatlock;	/* lockmgr protecting allocations */
+	struct lock pm_checkpath_lock; /* protects doscheckpath result */
 #endif
 };