linux-kernel - [PATCH 4.11 45/84] ovl: copy-up: dont unlock between lookup and link

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Date:   Mon,  3 Jul 2017 15:35:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>
Subject: [PATCH 4.11 45/84] ovl: copy-up: dont unlock between lookup and link

4.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@...hat.com>

commit e85f82ff9b8ef503923a3be8ca6b5fd1908a7f3f upstream.

Nothing prevents mischief on upper layer while we are busy copying up the
data.

Move the lookup right before the looked up dentry is actually used.

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Fixes: 01ad3eb8a073 ("ovl: concurrent copy up of regular files")
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/overlayfs/copy_up.c |   24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -252,15 +252,9 @@ static int ovl_copy_up_locked(struct den
 		.link = link
 	};
 
-	upper = lookup_one_len(dentry->d_name.name, upperdir,
-			       dentry->d_name.len);
-	err = PTR_ERR(upper);
-	if (IS_ERR(upper))
-		goto out;
-
 	err = security_inode_copy_up(dentry, &new_creds);
 	if (err < 0)
-		goto out1;
+		goto out;
 
 	if (new_creds)
 		old_creds = override_creds(new_creds);
@@ -284,7 +278,7 @@ static int ovl_copy_up_locked(struct den
 	}
 
 	if (err)
-		goto out2;
+		goto out;
 
 	if (S_ISREG(stat->mode)) {
 		struct path upperpath;
@@ -317,6 +311,14 @@ static int ovl_copy_up_locked(struct den
 	if (err)
 		goto out_cleanup;
 
+	upper = lookup_one_len(dentry->d_name.name, upperdir,
+			       dentry->d_name.len);
+	if (IS_ERR(upper)) {
+		err = PTR_ERR(upper);
+		upper = NULL;
+		goto out_cleanup;
+	}
+
 	if (tmpfile)
 		err = ovl_do_link(temp, udir, upper, true);
 	else
@@ -330,17 +332,15 @@ static int ovl_copy_up_locked(struct den
 
 	/* Restore timestamps on parent (best effort) */
 	ovl_set_timestamps(upperdir, pstat);
-out2:
+out:
 	dput(temp);
-out1:
 	dput(upper);
-out:
 	return err;
 
 out_cleanup:
 	if (!tmpfile)
 		ovl_cleanup(wdir, temp);
-	goto out2;
+	goto out;
 }
 
 /*