linux-kernel - [PATCH][capabilities-next] commoncap: move assignment of fs

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Message-Id: <20170904175005.29871-1-colin.king@canonical.com>
Date:   Mon,  4 Sep 2017 18:50:05 +0100
From:   Colin King <colin.king@...onical.com>
To:     Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>,
        linux-security-module@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][capabilities-next] commoncap: move assignment of fs_ns to avoid null pointer dereference

From: Colin Ian King <colin.king@...onical.com>

The pointer fs_ns is assigned from inode->i_ib->s_user_ns before
a null pointer check on inode, hence if inode is actually null we
will get a null pointer dereference on this assignment. Fix this
by only dereferencing inode after the null pointer check on
inode.

Detected by CoverityScan CID#1455328 ("Dereference before null check")

Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 security/commoncap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/commoncap.c b/security/commoncap.c
index c25e0d27537f..fc46f5b85251 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -585,13 +585,14 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
 	struct vfs_ns_cap_data data, *nscaps = &data;
 	struct vfs_cap_data *caps = (struct vfs_cap_data *) &data;
 	kuid_t rootkuid;
-	struct user_namespace *fs_ns = inode->i_sb->s_user_ns;
+	struct user_namespace *fs_ns;
 
 	memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data));
 
 	if (!inode)
 		return -ENODATA;
 
+	fs_ns = inode->i_sb->s_user_ns;
 	size = __vfs_getxattr((struct dentry *)dentry, inode,
 			      XATTR_NAME_CAPS, &data, XATTR_CAPS_SZ);
 	if (size == -ENODATA || size == -EOPNOTSUPP)
-- 
2.14.1