git: b393aa8e30b5 - stable/15 - nullfs: do not allow to mount a vnode over itself

The branch stable/15 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=b393aa8e30b5911a5177b6aaacd5a62beea8e3d6

commit b393aa8e30b5911a5177b6aaacd5a62beea8e3d6
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2026-05-16 22:16:45 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2026-05-23 06:56:13 +0000

    nullfs: do not allow to mount a vnode over itself
    
    PR:     275570
    
    (cherry picked from commit 7bdf2b5d5fbabfc8749c4ff6e618c3e843b14de0)
---
 sys/fs/nullfs/null_vfsops.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
index c3eec727aeea..0ec4f9c87297 100644
--- a/sys/fs/nullfs/null_vfsops.c
+++ b/sys/fs/nullfs/null_vfsops.c
@@ -151,6 +151,14 @@ nullfs_mount(struct mount *mp)
 	 */
 	lowerrootvp = ndp->ni_vp;
 
+	/*
+	 * Do not allow to mount a vnode over itself.
+	 */
+	if (mp->mnt_vnodecovered == lowerrootvp) {
+		vput(lowerrootvp);
+		return (EDEADLK);
+	}
+
 	/*
 	 * Check multi null mount to avoid `lock against myself' panic.
 	 */