linux-kernel - [PATCH] fs: Reorder inode_owner_or

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Message-ID: <20170620214024.GA121654@beast>
Date:   Tue, 20 Jun 2017 14:40:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Solar Designer <solar@...nwall.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs: Reorder inode_owner_or_capable() to avoid needless

Checking for capabilities should be the last operation when performing
access control tests so that PF_SUPERPRIV is set only when it was required
for success (implying that the capability was needed for the operation).

Reported-by: Solar Designer <solar@...nwall.com>
Cc: Serge E. Hallyn <serge@...lyn.com>
Cc: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/inode.c | 2 +-
 fs/namei.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index db5914783a71..7092debe90cc 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2023,7 +2023,7 @@ bool inode_owner_or_capable(const struct inode *inode)
 		return true;
 
 	ns = current_user_ns();
-	if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
+	if (kuid_has_mapping(ns, inode->i_uid) && ns_capable(ns, CAP_FOWNER))
 		return true;
 	return false;
 }
diff --git a/fs/namei.c b/fs/namei.c
index 6571a5f5112e..efe53a5d0737 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1008,7 +1008,7 @@ static int may_linkat(struct path *link)
 	/* Source inode owner (or CAP_FOWNER) can hardlink all they like,
 	 * otherwise, it must be a safe source.
 	 */
-	if (inode_owner_or_capable(inode) || safe_hardlink_source(inode))
+	if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
 		return 0;
 
 	audit_log_link_denied("linkat", link);
-- 
2.7.4


-- 
Kees Cook
Pixel Security