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

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Date:   Mon, 4 Sep 2017 13:53:39 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>,
        linux-security-module@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][capabilities-next] commoncap: move assignment of fs_ns
 to avoid null pointer dereference

On Mon, Sep 04, 2017 at 06:50:05PM +0100, Colin King wrote:
> 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>

thanks!

Acked-by: Serge Hallyn <serge@...lyn.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