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Date:   Sun, 15 Oct 2023 18:29:27 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     linux-nfs@vger.kernel.org
Subject: [PATCH] nfsd: lock_rename() needs both directories to live on the
 same fs
Message-ID: <20231015172927.GE800259@ZenIV>
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Sender: Al Viro <viro@ftp.linux.org.uk>
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... checking that after lock_rename() is too late.  Incidentally,
NFSv2 had no nfserr_xdev...

Fixes: aa387d6ce153 "nfsd: fix EXDEV checking in rename"
Cc: stable@vger.kernel.org # v3.9+
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

[in git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #nfsd-fix;
it's an immutable branch, please either pull from it or put that thing
into an immutable branch in your tree - there's a lock_rename-related
series in the making and I'd rather avoid mixing unrelated nfsd stuff
into it ;-/]

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 48260cf68fde..02f5fcaad03f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1788,6 +1788,12 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 	if (!flen || isdotent(fname, flen) || !tlen || isdotent(tname, tlen))
 		goto out;
 
+	err = (rqstp->rq_vers == 2) ? nfserr_acces : nfserr_xdev;
+	if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
+		goto out;
+	if (ffhp->fh_export->ex_path.dentry != tfhp->fh_export->ex_path.dentry)
+		goto out;
+
 retry:
 	host_err = fh_want_write(ffhp);
 	if (host_err) {
@@ -1823,12 +1829,6 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 	if (ndentry == trap)
 		goto out_dput_new;
 
-	host_err = -EXDEV;
-	if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
-		goto out_dput_new;
-	if (ffhp->fh_export->ex_path.dentry != tfhp->fh_export->ex_path.dentry)
-		goto out_dput_new;
-
 	if ((ndentry->d_sb->s_export_op->flags & EXPORT_OP_CLOSE_BEFORE_UNLINK) &&
 	    nfsd_has_cached_files(ndentry)) {
 		close_cached = true;