Re: [PATCH v35 08/29] LSM: Use lsmblob in security_secctx_to_secid

John Johansen
2022-04-27T00:39:20Z

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);
>