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From:   Stanislav Goriainov <goriainov@ispras.ru>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Stanislav Goriainov <goriainov@ispras.ru>,
        Vivek Goyal <vgoyal@redhat.com>,
        Amir Goldstein <amir73il@gmail.com>,
        linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        ldv-project@linuxtesting.org
Subject: [PATCH v2] ovl: Add comment on upperredirect reassignment
Date:   Wed, 31 Aug 2022 11:06:58 +0300
Message-Id: <20220831080658.14878-1-goriainov@ispras.ru>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

If memory for uperredirect was allocated with kstrdup()
in upperdir != NULL and d.redirect != NULL path, it may seem
that it can be lost when upperredirect is reassigned later, but
it's not possible.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 0a2d0d3f2f291 ("ovl: Check redirect on index as well")
Signed-off-by: Stanislav Goriainov <goriainov@ispras.ru>
---
 fs/overlayfs/namei.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 69dc577974f8..2a21331e6ccd 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -1085,6 +1085,11 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			.mnt = ovl_upper_mnt(ofs),
 		};
 
+		/* There is no overwrite of upperredirect here as the first
+		 * assignment of upperredirect happens only if
+		 * upperdentry is non-NULL, while here we are only
+		 * if upperdentry is NULL.
+		 */
 		upperredirect = ovl_get_redirect_xattr(ofs, &upperpath, 0);
 		if (IS_ERR(upperredirect)) {
 			err = PTR_ERR(upperredirect);
-- 
2.34.1