Subject: Re: Possible fix

From: Steffen Klassert <[email-masked]>
Date: Fri, 28 Feb 2014 08:23:33 +0100

Ccing some security/selinux people.

On Thu, Feb 27, 2014 at 05:17:37PM +0100, Nikolay Aleksandrov wrote:
> Hi,
> I'm not familiar with the code but happened to see the bug, could you
> try the following patch, I believe it should fix the issue.
> 
> Thanks,
>  Nik
> 
> [PATCH net] net: af_key: fix sleeping under rcu
> 
> There's a kmalloc with GFP_KERNEL in a helper
> (pfkey_sadb2xfrm_user_sec_ctx) used in pfkey_compile_policy which is
> called under rcu_read_lock. Adjust pfkey_sadb2xfrm_user_sec_ctx to have
> a gfp argument and adjust the users.
> 

Looking at the git history, it seems that this bug is about nine
years old. I guess noone is actually using this.

Also, we care for the security context only if we add a socket
policy via the pfkey key manager. The security context is not
handled if we do that with the netlink key manager
(compare pfkey_compile_policy() and xfrm_compile_policy()).

> CC: Dave Jones <[email-masked]>
> CC: Steffen Klassert <[email-masked]>
> CC: Fan Du <[email-masked]>
> CC: David S. Miller <[email-masked]>
> 
> Signed-off-by: Nikolay Aleksandrov <[email-masked]>
> ---
> I'm not familiar with this code, but just happen to see the bug. I believe
> this patch should take care of it.
> I've left the already very long lines.
> 
>  net/key/af_key.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/net/key/af_key.c b/net/key/af_key.c
> index 1a04c1329362..1526023f99ed 100644
> --- a/net/key/af_key.c
> +++ b/net/key/af_key.c
> @@ -433,12 +433,13 @@ static inline int verify_sec_ctx_len(const void *p)
>  	return 0;
>  }
>  
> -static inline struct xfrm_user_sec_ctx *pfkey_sadb2xfrm_user_sec_ctx(const struct sadb_x_sec_ctx *sec_ctx)
> +static inline struct xfrm_user_sec_ctx *pfkey_sadb2xfrm_user_sec_ctx(const struct sadb_x_sec_ctx *sec_ctx,
> +								     gfp_t gfp)
>  {
>  	struct xfrm_user_sec_ctx *uctx = NULL;
>  	int ctx_size = sec_ctx->sadb_x_ctx_len;
>  
> -	uctx = kmalloc((sizeof(*uctx)+ctx_size), GFP_KERNEL);
> +	uctx = kmalloc((sizeof(*uctx)+ctx_size), gfp);
>  
>  	if (!uctx)
>  		return NULL;
> @@ -1124,7 +1125,7 @@ static struct xfrm_state * pfkey_msg2xfrm_state(struct net *net,
>  
>  	sec_ctx = ext_hdrs[SADB_X_EXT_SEC_CTX - 1];
>  	if (sec_ctx != NULL) {
> -		struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
> +		struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx, GFP_KERNEL);
>  
>  		if (!uctx)
>  			goto out;
> @@ -2231,7 +2232,7 @@ static int pfkey_spdadd(struct sock *sk, struct sk_buff *skb, const struct sadb_
>  
>  	sec_ctx = ext_hdrs[SADB_X_EXT_SEC_CTX - 1];
>  	if (sec_ctx != NULL) {
> -		struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
> +		struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx, GFP_KERNEL);
>  
>  		if (!uctx) {
>  			err = -ENOBUFS;
> @@ -2335,7 +2336,7 @@ static int pfkey_spddelete(struct sock *sk, struct sk_buff *skb, const struct sa
>  
>  	sec_ctx = ext_hdrs[SADB_X_EXT_SEC_CTX - 1];
>  	if (sec_ctx != NULL) {
> -		struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
> +		struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx, GFP_KERNEL);
>  
>  		if (!uctx)
>  			return -ENOMEM;
> @@ -3239,7 +3240,7 @@ static struct xfrm_policy *pfkey_compile_policy(struct sock *sk, int opt,
>  		}
>  		if ((*dir = verify_sec_ctx_len(p)))
>  			goto out;
> -		uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
> +		uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx, GFP_ATOMIC);
>  		*dir = security_xfrm_policy_alloc(&xp->security, uctx);

This would fix the allocation done in pfkey_sadb2xfrm_user_sec_ctx().
But security_xfrm_policy_alloc() might call selinux_xfrm_alloc_user()
which does a GFP_KERNEL allocation too. So I guess we also need to fix
selinux.