selinux January 2010 archive
Main Archive Page > Month Archives  > selinux archives
selinux: Re: [RFC PATCH v3] selinux: Fix security_compute_av() t

Re: [RFC PATCH v3] selinux: Fix security_compute_av() to not return unknown class errors when in permissive mode

From: Stephen Smalley <sds_at_nospam>
Date: Mon Jan 04 2010 - 21:11:37 GMT
To: Paul Moore <paul.moore@hp.com>


On Fri, 2009-12-18 at 13:30 -0500, Paul Moore wrote:
> It is possible security_compute_av() to return -EINVAL, even when in
> permissive mode, due to unknown object classes and SIDs. This patch fixes
> this by doing away with the return value for security_compute_av() and
> treating unknown classes and SIDs as permission denials.
>
> NOTE: This patch has only been compile tested, and is only intended for
> review. However, if someone wants to give it a try I would appreciate it
> as my time is somewhat limited since I'm technically on "vacation" as of a
> few hours ago :)
>
> Reported-by: Andrew Worsley <amworsley@gmail.com>
> Signed-off-by: Paul Moore <paul.moore@hp.com>

NAK. Sorry, but I think we need to reconsider this patch, as separating the initialization of the avd from the remainder of the computation inside of context_struct_compute_av is fragile, as is separating the printk error message from the actual error checking (and allow_unknown isn't relevant in that particular case - we have already covered it after we unmap the class).

> ---
> security/selinux/avc.c | 14 ++--
> security/selinux/include/security.h | 8 +-
> security/selinux/selinuxfs.c | 4 +
> security/selinux/ss/services.c | 113 +++++++++++++----------------------
> 4 files changed, 54 insertions(+), 85 deletions(-)
>
> diff --git a/security/selinux/avc.c b/security/selinux/avc.c
> index f2dde26..7471a0a 100644
> --- a/security/selinux/avc.c
> +++ b/security/selinux/avc.c
> @@ -731,7 +731,6 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
> struct avc_node *node;
> struct av_decision avd_entry, *avd;
> int rc = 0;
> - u32 denied;
>
> BUG_ON(!requested);
>
> @@ -746,9 +745,7 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
> else
> avd = &avd_entry;
>
> - rc = security_compute_av(ssid, tsid, tclass, requested, avd);
> - if (rc)
> - goto out;
> + security_compute_av(ssid, tsid, tclass, avd);
> rcu_read_lock();
> node = avc_insert(ssid, tsid, tclass, avd);
> } else {
> @@ -757,12 +754,11 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
> avd = &node->ae.avd;
> }
>
> - denied = requested & ~(avd->allowed);
> -
> - if (denied) {
> + if (requested & ~(avd->allowed)) {
> if (flags & AVC_STRICT)
> rc = -EACCES;
> - else if (!selinux_enforcing || (avd->flags & AVD_FLAGS_PERMISSIVE))
> + else if (!selinux_enforcing ||
> + (avd->flags & AVD_FLAGS_PERMISSIVE))
> avc_update_node(AVC_CALLBACK_GRANT, requested, ssid,
> tsid, tclass, avd->seqno);
> else
> @@ -770,7 +766,7 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
> }
>
> rcu_read_unlock();
> -out:
> +
> return rc;
> }
>
> diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
> index 2553266..609334d 100644
> --- a/security/selinux/include/security.h
> +++ b/security/selinux/include/security.h
> @@ -96,12 +96,10 @@ struct av_decision {
> /* definitions of av_decision.flags */
> #define AVD_FLAGS_PERMISSIVE 0x0001
>
> -int security_compute_av(u32 ssid, u32 tsid,
> - u16 tclass, u32 requested,
> - struct av_decision *avd);
> +void security_compute_av(u32 ssid, u32 tsid, u16 tclass,
> + struct av_decision *avd);
>
> -int security_compute_av_user(u32 ssid, u32 tsid,
> - u16 tclass, u32 requested,
> +int security_compute_av_user(u32 ssid, u32 tsid, u16 tclass,
> struct av_decision *avd);
>
> int security_transition_sid(u32 ssid, u32 tsid,
> diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> index fab36fd..a45ac7c 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -511,6 +511,8 @@ static ssize_t sel_write_access(struct file *file, char *buf, size_t size)
> if (!tcon)
> goto out;
>
> + /* note: we don't currently use "req" anymore but we'll leave it here
> + * just to preserve/enforce the existing userspace API */
> length = -EINVAL;
> if (sscanf(buf, "%s %s %hu %x", scon, tcon, &tclass, &req) != 4)
> goto out2;
> @@ -522,7 +524,7 @@ static ssize_t sel_write_access(struct file *file, char *buf, size_t size)
> if (length < 0)
> goto out2;
>
> - length = security_compute_av_user(ssid, tsid, tclass, req, &avd);
> + length = security_compute_av_user(ssid, tsid, tclass, &avd);
> if (length < 0)
> goto out2;
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index b3efae2..e789b34 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -90,7 +90,6 @@ static int context_struct_to_string(struct context *context, char **scontext,
> static int context_struct_compute_av(struct context *scontext,
> struct context *tcontext,
> u16 tclass,
> - u32 requested,
> struct av_decision *avd);
>
> struct selinux_mapping {
> @@ -196,23 +195,6 @@ static u16 unmap_class(u16 tclass)
> return tclass;
> }
>
> -static u32 unmap_perm(u16 tclass, u32 tperm)
> -{
> - if (tclass < current_mapping_size) {
> - unsigned i;
> - u32 kperm = 0;
> -
> - for (i = 0; i < current_mapping[tclass].num_perms; i++)
> - if (tperm & (1<<i)) {
> - kperm |= current_mapping[tclass].perms[i];
> - tperm &= ~(1<<i);
> - }
> - return kperm;
> - }
> -
> - return tperm;
> -}
> -
> static void map_decision(u16 tclass, struct av_decision *avd,
> int allow_unknown)
> {
> @@ -532,7 +514,6 @@ out:
> static void type_attribute_bounds_av(struct context *scontext,
> struct context *tcontext,
> u16 tclass,
> - u32 requested,
> struct av_decision *avd)
> {
> struct context lo_scontext;
> @@ -553,7 +534,6 @@ static void type_attribute_bounds_av(struct context *scontext,
> context_struct_compute_av(&lo_scontext,
> tcontext,
> tclass,
> - requested,
> &lo_avd);
> if ((lo_avd.allowed & avd->allowed) == avd->allowed)
> return; /* no masked permission */
> @@ -569,7 +549,6 @@ static void type_attribute_bounds_av(struct context *scontext,
> context_struct_compute_av(scontext,
> &lo_tcontext,
> tclass,
> - requested,
> &lo_avd);
> if ((lo_avd.allowed & avd->allowed) == avd->allowed)
> return; /* no masked permission */
> @@ -586,7 +565,6 @@ static void type_attribute_bounds_av(struct context *scontext,
> context_struct_compute_av(&lo_scontext,
> &lo_tcontext,
> tclass,
> - requested,
> &lo_avd);
> if ((lo_avd.allowed & avd->allowed) == avd->allowed)
> return; /* no masked permission */
> @@ -610,7 +588,6 @@ static void type_attribute_bounds_av(struct context *scontext,
> static int context_struct_compute_av(struct context *scontext,
> struct context *tcontext,
> u16 tclass,
> - u32 requested,
> struct av_decision *avd)
> {
> struct constraint_node *constraint;
> @@ -622,20 +599,8 @@ static int context_struct_compute_av(struct context *scontext,
> struct ebitmap_node *snode, *tnode;
> unsigned int i, j;
>
> - /*
> - * Initialize the access vectors to the default values.
> - */
> - avd->allowed = 0;
> - avd->auditallow = 0;
> - avd->auditdeny = 0xffffffff;
> - avd->seqno = latest_granting;
> - avd->flags = 0;
> -
> - if (unlikely(!tclass || tclass > policydb.p_classes.nprim)) {
> - if (printk_ratelimit())
> - printk(KERN_WARNING "SELinux: Invalid class %hu\n", tclass);
> + if (unlikely(!tclass || tclass > policydb.p_classes.nprim))
> return -EINVAL;
> - }
>
> tclass_datum = policydb.class_val_to_struct[tclass - 1];
>
> @@ -704,8 +669,7 @@ static int context_struct_compute_av(struct context *scontext,
> * constraint, lazy checks have to mask any violated
> * permission and notice it to userspace via audit.
> */
> - type_attribute_bounds_av(scontext, tcontext,
> - tclass, requested, avd);
> + type_attribute_bounds_av(scontext, tcontext, tclass, avd);
>
> return 0;
> }
> @@ -890,11 +854,11 @@ out:
> static int security_compute_av_core(u32 ssid,
> u32 tsid,
> u16 tclass,
> - u32 requested,
> + int allow_unknown,
> struct av_decision *avd)
> {
> struct context *scontext = NULL, *tcontext = NULL;
> - int rc = 0;
> + int rc;
>
> scontext = sidtab_search(&sidtab, ssid);
> if (!scontext) {
> @@ -909,8 +873,9 @@ static int security_compute_av_core(u32 ssid,
> return -EINVAL;
> }
>
> - rc = context_struct_compute_av(scontext, tcontext, tclass,
> - requested, avd);
> + rc = context_struct_compute_av(scontext, tcontext, tclass, avd);
> + if (rc == -EINVAL && !allow_unknown && printk_ratelimit())
> + printk(KERN_WARNING "SELinux: Invalid class %hu\n", tclass);
>
> /* permissive domain? */
> if (ebitmap_get_bit(&policydb.permissive_map, scontext->type))
> @@ -924,70 +889,78 @@ static int security_compute_av_core(u32 ssid,
> * @ssid: source security identifier
> * @tsid: target security identifier
> * @tclass: target security class
> - * @requested: requested permissions
> * @avd: access vector decisions
> *
> * Compute a set of access vector decisions based on the
> * SID pair (@ssid, @tsid) for the permissions in @tclass.
> - * Return -%EINVAL if any of the parameters are invalid or %0
> - * if the access vector decisions were computed successfully.
> */
> -int security_compute_av(u32 ssid,
> - u32 tsid,
> - u16 orig_tclass,
> - u32 orig_requested,
> - struct av_decision *avd)
> +void security_compute_av(u32 ssid,
> + u32 tsid,
> + u16 orig_tclass,
> + struct av_decision *avd)
> {
> u16 tclass;
> - u32 requested;
> int rc;
>
> read_lock(&policy_rwlock);
>
> + /* Initialize the access vectors to the default values. */
> + avd->allowed = 0;
> + avd->auditallow = 0;
> + avd->auditdeny = 0xffffffff;
> + avd->seqno = latest_granting;
> + avd->flags = 0;
> +
> if (!ss_initialized)
> goto allow;
>
> - requested = unmap_perm(orig_tclass, orig_requested);
> tclass = unmap_class(orig_tclass);
> - if (unlikely(orig_tclass && !tclass)) {
> - if (policydb.allow_unknown)
> - goto allow;
> - rc = -EINVAL;
> - goto out;
> - }
> - rc = security_compute_av_core(ssid, tsid, tclass, requested, avd);
> + if (unlikely(orig_tclass && !tclass))
> + goto error;
> + rc = security_compute_av_core(ssid, tsid, tclass,
> + policydb.allow_unknown, avd);
> + if (unlikely(rc != 0))
> + goto error;
> map_decision(orig_tclass, avd, policydb.allow_unknown);
> out:
> read_unlock(&policy_rwlock);
> - return rc;
> + return;
> allow:
> avd->allowed = 0xffffffff;
> + goto out;
> +error:
> + if (policydb.allow_unknown)
> + goto allow;
> + avd->allowed = 0;
> avd->auditallow = 0;
> avd->auditdeny = 0xffffffff;
> - avd->seqno = latest_granting;
> - avd->flags = 0;
> - rc = 0;
> goto out;
> }
>
> int security_compute_av_user(u32 ssid,
> u32 tsid,
> u16 tclass,
> - u32 requested,
> struct av_decision *avd)
> {
> int rc;
>
> + read_lock(&policy_rwlock);
> +
> + /* Initialize the access vectors to the default values. */
> + avd->allowed = 0;
> + avd->auditallow = 0;
> + avd->auditdeny = 0xffffffff;
> + avd->seqno = latest_granting;
> + avd->flags = 0;
> +
> if (!ss_initialized) {
> avd->allowed = 0xffffffff;
> - avd->auditallow = 0;
> - avd->auditdeny = 0xffffffff;
> - avd->seqno = latest_granting;
> - return 0;
> + rc = 0;
> + goto out;
> }
>
> - read_lock(&policy_rwlock);
> - rc = security_compute_av_core(ssid, tsid, tclass, requested, avd);
> + rc = security_compute_av_core(ssid, tsid, tclass, 0, avd);
> +out:
> read_unlock(&policy_rwlock);
> return rc;
> }
>
>
> --
> This message was distributed to subscribers of the selinux mailing list.
> If you no longer wish to subscribe, send mail to majordomo@tycho.nsa.gov with
> the words "unsubscribe selinux" without quotes as the message.
-- Stephen Smalley National Security Agency -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@tycho.nsa.gov with the words "unsubscribe selinux" without quotes as the message.