From a5970a529c2d952714f20e4bc6e529c74fd2b3b5 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 3 Apr 2021 21:55:11 +0300
Subject: [PATCH] Make files opened with O_PATH to not block non-forced unmount

by only keeping hold count on the vnode, instead of the use count.

Reviewed by:	markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D29323
---
 lib/libc/sys/open.2     |  3 +++
 sys/kern/kern_descrip.c |  6 +++---
 sys/kern/vfs_lookup.c   |  2 +-
 sys/kern/vfs_syscalls.c | 11 ++++++++---
 4 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/lib/libc/sys/open.2 b/lib/libc/sys/open.2
index f9c54bfc7581..06a877e34460 100644
--- a/lib/libc/sys/open.2
+++ b/lib/libc/sys/open.2
@@ -349,6 +349,9 @@ But operations like
 and any other that operate on file and not on file descriptor (except
 .Xr fstat 2 ),
 are not allowed.
+File opened with the
+.Dv O_PATH
+flag does not prevent non-forced unmount of the volume it belongs to.
 See also the description of
 .Dv AT_EMPTY_PATH
 flag for
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 81af58fbddd1..a28e94634326 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -3430,7 +3430,7 @@ _fgetvp(struct thread *td, int fd, int flags, cap_rights_t *needrightsp,
 		error = EINVAL;
 	} else {
 		*vpp = fp->f_vnode;
-		vrefact(*vpp);
+		vref(*vpp);
 	}
 	fdrop(fp, td);
 
@@ -3466,7 +3466,7 @@ fgetvp_rights(struct thread *td, int fd, cap_rights_t *needrightsp,
 
 	*havecaps = caps;
 	*vpp = fp->f_vnode;
-	vrefact(*vpp);
+	vref(*vpp);
 	fdrop(fp, td);
 
 	return (0);
@@ -4978,7 +4978,7 @@ path_close(struct file *fp, struct thread *td)
 {
 	MPASS(fp->f_type == DTYPE_VNODE);
 	fp->f_ops = &badfileops;
-	vrele(fp->f_vnode);
+	vdrop(fp->f_vnode);
 	return (0);
 }
 
diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index f979676f4c7d..3050275c1b6f 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -380,7 +380,7 @@ namei_setup(struct nameidata *ndp, struct vnode **dpp, struct pwd **pwdp)
 					error = ENOTDIR;
 				} else {
 					*dpp = dfp->f_vnode;
-					vrefact(*dpp);
+					vref(*dpp);
 
 					if ((dfp->f_flag & FSEARCH) != 0)
 						cnp->cn_flags |= NOEXECCHECK;
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 5a1efcdec467..9130843f6761 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -896,7 +896,7 @@ sys_fchdir(struct thread *td, struct fchdir_args *uap)
 	if (error != 0)
 		return (error);
 	vp = fp->f_vnode;
-	vrefact(vp);
+	vref(vp);
 	fdrop(fp, td);
 	vn_lock(vp, LK_SHARED | LK_RETRY);
 	AUDIT_ARG_VNODE1(vp);
@@ -1191,8 +1191,13 @@ kern_openat(struct thread *td, int fd, const char *path, enum uio_seg pathseg,
 	if (fp->f_ops == &badfileops) {
 		KASSERT(vp->v_type != VFIFO || (flags & O_PATH) != 0,
 		    ("Unexpected fifo fp %p vp %p", fp, vp));
-		finit_vnode(fp, flags, NULL, (flags & O_PATH) != 0 ?
-		    &path_fileops : &vnops);
+		if ((flags & O_PATH) != 0) {
+			finit_vnode(fp, flags, NULL, &path_fileops);
+			vhold(vp);
+			vunref(vp);
+		} else {
+			finit_vnode(fp, flags, NULL, &vnops);
+		}
 	}
 
 	VOP_UNLOCK(vp);