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Message-ID: <1795819d-661a-3859-39e2-ba17a84508dd@canonical.com>
Date:   Tue, 26 Apr 2022 17:38:55 -0700
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Subject: Re: [PATCH v35 08/29] LSM: Use lsmblob in security_secctx_to_secid
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To:     Casey Schaufler <casey@schaufler-ca.com>,
        casey.schaufler@intel.com, jmorris@namei.org,
        linux-security-module@vger.kernel.org, selinux@vger.kernel.org
Cc:     linux-audit@redhat.com, keescook@chromium.org,
        penguin-kernel@i-love.sakura.ne.jp, paul@paul-moore.com,
        stephen.smalley.work@gmail.com, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, netfilter-devel@vger.kernel.org
References: <20220418145945.38797-1-casey@schaufler-ca.com>
 <20220418145945.38797-9-casey@schaufler-ca.com>
From:   John Johansen <john.johansen@canonical.com>
Organization: Canonical
In-Reply-To: <20220418145945.38797-9-casey@schaufler-ca.com>
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Precedence: bulk

On 4/18/22 07:59, Casey Schaufler wrote:
> Change the security_secctx_to_secid interface to use a lsmblob
> structure in place of the single u32 secid in support of
> module stacking. Change its callers to do the same.
> 
> The security module hook is unchanged, still passing back a secid.
> The infrastructure passes the correct entry from the lsmblob.
> 
> Acked-by: Paul Moore <paul@paul-moore.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Cc: netdev@vger.kernel.org
> Cc: netfilter-devel@vger.kernel.org
> To: Pablo Neira Ayuso <pablo@netfilter.org>

Reviewed-by: John Johansen <john.johansen@canonical.com>

> ---
>  include/linux/security.h          | 26 ++++++++++++++++++--
>  kernel/cred.c                     |  4 +---
>  net/netfilter/nft_meta.c          | 10 ++++----
>  net/netfilter/xt_SECMARK.c        |  7 +++++-
>  net/netlabel/netlabel_unlabeled.c | 23 +++++++++++-------
>  security/security.c               | 40 ++++++++++++++++++++++++++-----
>  6 files changed, 85 insertions(+), 25 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 68ab0add23d3..57879f0b9f89 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -199,6 +199,27 @@ static inline bool lsmblob_equal(const struct lsmblob *bloba,
>  extern int lsm_name_to_slot(char *name);
>  extern const char *lsm_slot_to_name(int slot);
>  
> +/**
> + * lsmblob_value - find the first non-zero value in an lsmblob structure.
> + * @blob: Pointer to the data
> + *
> + * This needs to be used with extreme caution, as the cases where
> + * it is appropriate are rare.
> + *
> + * Return the first secid value set in the lsmblob.
> + * There should only be one.
> + */
> +static inline u32 lsmblob_value(const struct lsmblob *blob)
> +{
> +	int i;
> +
> +	for (i = 0; i < LSMBLOB_ENTRIES; i++)
> +		if (blob->secid[i])
> +			return blob->secid[i];
> +
> +	return 0;
> +}
> +
>  /* These functions are in security/commoncap.c */
>  extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
>  		       int cap, unsigned int opts);
> @@ -529,7 +550,8 @@ int security_setprocattr(const char *lsm, const char *name, void *value,
>  int security_netlink_send(struct sock *sk, struct sk_buff *skb);
>  int security_ismaclabel(const char *name);
>  int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen);
> -int security_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid);
> +int security_secctx_to_secid(const char *secdata, u32 seclen,
> +			     struct lsmblob *blob);
>  void security_release_secctx(char *secdata, u32 seclen);
>  void security_inode_invalidate_secctx(struct inode *inode);
>  int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
> @@ -1384,7 +1406,7 @@ static inline int security_secid_to_secctx(u32 secid, char **secdata, u32 *secle
>  
>  static inline int security_secctx_to_secid(const char *secdata,
>  					   u32 seclen,
> -					   u32 *secid)
> +					   struct lsmblob *blob)
>  {
>  	return -EOPNOTSUPP;
>  }
> diff --git a/kernel/cred.c b/kernel/cred.c
> index 3925d38f49f4..adea727744f4 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -791,14 +791,12 @@ EXPORT_SYMBOL(set_security_override);
>  int set_security_override_from_ctx(struct cred *new, const char *secctx)
>  {
>  	struct lsmblob blob;
> -	u32 secid;
>  	int ret;
>  
> -	ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
> +	ret = security_secctx_to_secid(secctx, strlen(secctx), &blob);
>  	if (ret < 0)
>  		return ret;
>  
> -	lsmblob_init(&blob, secid);
>  	return set_security_override(new, &blob);
>  }
>  EXPORT_SYMBOL(set_security_override_from_ctx);
> diff --git a/net/netfilter/nft_meta.c b/net/netfilter/nft_meta.c
> index ac4859241e17..fc0028c9e33d 100644
> --- a/net/netfilter/nft_meta.c
> +++ b/net/netfilter/nft_meta.c
> @@ -860,21 +860,21 @@ static const struct nla_policy nft_secmark_policy[NFTA_SECMARK_MAX + 1] = {
>  
>  static int nft_secmark_compute_secid(struct nft_secmark *priv)
>  {
> -	u32 tmp_secid = 0;
> +	struct lsmblob blob;
>  	int err;
>  
> -	err = security_secctx_to_secid(priv->ctx, strlen(priv->ctx), &tmp_secid);
> +	err = security_secctx_to_secid(priv->ctx, strlen(priv->ctx), &blob);
>  	if (err)
>  		return err;
>  
> -	if (!tmp_secid)
> +	if (!lsmblob_is_set(&blob))
>  		return -ENOENT;
>  
> -	err = security_secmark_relabel_packet(tmp_secid);
> +	err = security_secmark_relabel_packet(lsmblob_value(&blob));
>  	if (err)
>  		return err;
>  
> -	priv->secid = tmp_secid;
> +	priv->secid = lsmblob_value(&blob);
>  	return 0;
>  }
>  
> diff --git a/net/netfilter/xt_SECMARK.c b/net/netfilter/xt_SECMARK.c
> index 498a0bf6f044..87ca3a537d1c 100644
> --- a/net/netfilter/xt_SECMARK.c
> +++ b/net/netfilter/xt_SECMARK.c
> @@ -42,13 +42,14 @@ secmark_tg(struct sk_buff *skb, const struct xt_secmark_target_info_v1 *info)
>  
>  static int checkentry_lsm(struct xt_secmark_target_info_v1 *info)
>  {
> +	struct lsmblob blob;
>  	int err;
>  
>  	info->secctx[SECMARK_SECCTX_MAX - 1] = '\0';
>  	info->secid = 0;
>  
>  	err = security_secctx_to_secid(info->secctx, strlen(info->secctx),
> -				       &info->secid);
> +				       &blob);
>  	if (err) {
>  		if (err == -EINVAL)
>  			pr_info_ratelimited("invalid security context \'%s\'\n",
> @@ -56,6 +57,10 @@ static int checkentry_lsm(struct xt_secmark_target_info_v1 *info)
>  		return err;
>  	}
>  
> +	/* xt_secmark_target_info can't be changed to use lsmblobs because
> +	 * it is exposed as an API. Use lsmblob_value() to get the one
> +	 * value that got set by security_secctx_to_secid(). */
> +	info->secid = lsmblob_value(&blob);
>  	if (!info->secid) {
>  		pr_info_ratelimited("unable to map security context \'%s\'\n",
>  				    info->secctx);
> diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
> index 8490e46359ae..f3e2cde76919 100644
> --- a/net/netlabel/netlabel_unlabeled.c
> +++ b/net/netlabel/netlabel_unlabeled.c
> @@ -880,7 +880,7 @@ static int netlbl_unlabel_staticadd(struct sk_buff *skb,
>  	void *addr;
>  	void *mask;
>  	u32 addr_len;
> -	u32 secid;
> +	struct lsmblob blob;
>  	struct netlbl_audit audit_info;
>  
>  	/* Don't allow users to add both IPv4 and IPv6 addresses for a
> @@ -904,13 +904,18 @@ static int netlbl_unlabel_staticadd(struct sk_buff *skb,
>  	ret_val = security_secctx_to_secid(
>  		                  nla_data(info->attrs[NLBL_UNLABEL_A_SECCTX]),
>  				  nla_len(info->attrs[NLBL_UNLABEL_A_SECCTX]),
> -				  &secid);
> +				  &blob);
>  	if (ret_val != 0)
>  		return ret_val;
>  
> +	/* netlbl_unlhsh_add will be changed to pass a struct lsmblob *
> +	 * instead of a u32 later in this patch set. security_secctx_to_secid()
> +	 * will only be setting one entry in the lsmblob struct, so it is
> +	 * safe to use lsmblob_value() to get that one value. */
> +
>  	return netlbl_unlhsh_add(&init_net,
> -				 dev_name, addr, mask, addr_len, secid,
> -				 &audit_info);
> +				 dev_name, addr, mask, addr_len,
> +				 lsmblob_value(&blob), &audit_info);
>  }
>  
>  /**
> @@ -931,7 +936,7 @@ static int netlbl_unlabel_staticadddef(struct sk_buff *skb,
>  	void *addr;
>  	void *mask;
>  	u32 addr_len;
> -	u32 secid;
> +	struct lsmblob blob;
>  	struct netlbl_audit audit_info;
>  
>  	/* Don't allow users to add both IPv4 and IPv6 addresses for a
> @@ -953,13 +958,15 @@ static int netlbl_unlabel_staticadddef(struct sk_buff *skb,
>  	ret_val = security_secctx_to_secid(
>  		                  nla_data(info->attrs[NLBL_UNLABEL_A_SECCTX]),
>  				  nla_len(info->attrs[NLBL_UNLABEL_A_SECCTX]),
> -				  &secid);
> +				  &blob);
>  	if (ret_val != 0)
>  		return ret_val;
>  
> +	/* security_secctx_to_secid() will only put one secid into the lsmblob
> +	 * so it's safe to use lsmblob_value() to get the secid. */
>  	return netlbl_unlhsh_add(&init_net,
> -				 NULL, addr, mask, addr_len, secid,
> -				 &audit_info);
> +				 NULL, addr, mask, addr_len,
> +				 lsmblob_value(&blob), &audit_info);
>  }
>  
>  /**
> diff --git a/security/security.c b/security/security.c
> index e9f1487af0e5..f814a41c5d9f 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2211,10 +2211,22 @@ int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
>  }
>  EXPORT_SYMBOL(security_secid_to_secctx);
>  
> -int security_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
> +int security_secctx_to_secid(const char *secdata, u32 seclen,
> +			     struct lsmblob *blob)
>  {
> -	*secid = 0;
> -	return call_int_hook(secctx_to_secid, 0, secdata, seclen, secid);
> +	struct security_hook_list *hp;
> +	int rc;
> +
> +	lsmblob_init(blob, 0);
> +	hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) {
> +		if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot))
> +			continue;
> +		rc = hp->hook.secctx_to_secid(secdata, seclen,
> +					      &blob->secid[hp->lsmid->slot]);
> +		if (rc != 0)
> +			return rc;
> +	}
> +	return 0;
>  }
>  EXPORT_SYMBOL(security_secctx_to_secid);
>  
> @@ -2365,10 +2377,26 @@ int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
>  				optval, optlen, len);
>  }
>  
> -int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
> +int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb,
> +				     u32 *secid)
>  {
> -	return call_int_hook(socket_getpeersec_dgram, -ENOPROTOOPT, sock,
> -			     skb, secid);
> +	struct security_hook_list *hp;
> +	int rc = -ENOPROTOOPT;
> +
> +	/*
> +	 * Only one security module should provide a real hook for
> +	 * this. A stub or bypass like is used in BPF should either
> +	 * (somehow) leave rc unaltered or return -ENOPROTOOPT.
> +	 */
> +	hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_dgram,
> +			     list) {
> +		if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot))
> +			continue;
> +		rc = hp->hook.socket_getpeersec_dgram(sock, skb, secid);
> +		if (rc != -ENOPROTOOPT)
> +			break;
> +	}
> +	return rc;
>  }
>  EXPORT_SYMBOL(security_socket_getpeersec_dgram);
>