[PATCH v3 1/2] selinux: add brief info to policydb
Roberts, William C
william.c.roberts at intel.com
Fri May 12 18:38:20 UTC 2017
> -----Original Message-----
> From: owner-linux-security-module at vger.kernel.org [mailto:owner-linux-
> security-module at vger.kernel.org] On Behalf Of Casey Schaufler
> Sent: Thursday, May 11, 2017 1:46 PM
> To: Stephen Smalley <sds at tycho.nsa.gov>; Sebastien Buisson
> <sbuisson.ddn at gmail.com>; linux-security-module at vger.kernel.org; linux-
> kernel at vger.kernel.org; selinux at tycho.nsa.gov
> Cc: Sebastien Buisson <sbuisson at ddn.com>; james.l.morris at oracle.com
> Subject: Re: [PATCH v3 1/2] selinux: add brief info to policydb
>
> On 5/11/2017 1:22 PM, Stephen Smalley wrote:
> > On Thu, 2017-05-11 at 08:56 -0700, Casey Schaufler wrote:
> >> On 5/11/2017 5:59 AM, Sebastien Buisson wrote:
> >>> Add policybrief field to struct policydb. It holds a brief info of
> >>> the policydb, in the following form:
> >>> <0 or 1 for enforce>:<0 or 1 for checkreqprot>:<hashalg>=<checksum>
> >>> Policy brief is computed every time the policy is loaded, and when
> >>> enforce or checkreqprot are changed.
> >>>
> >>> Add security_policy_brief hook to give access to policy brief to the
> >>> rest of the kernel. Lustre client makes use of this information to
> >>> detect changes to the policy, and forward it to Lustre servers.
> >>> Depending on how the policy is enforced on Lustre client side,
> >>> Lustre servers can refuse connection.
> >>>
> >>> Signed-off-by: Sebastien Buisson <sbuisson at ddn.com>
> >>> ---
> >>> include/linux/lsm_hooks.h | 16 ++++++++
> >>> include/linux/security.h | 7 ++++
> >>> security/security.c | 6 +++
> >>> security/selinux/hooks.c | 7 ++++
> >>> security/selinux/include/security.h | 2 +
> >>> security/selinux/selinuxfs.c | 2 +
> >>> security/selinux/ss/policydb.c | 76
> >>> +++++++++++++++++++++++++++++++++++++
> >>> security/selinux/ss/policydb.h | 2 +
> >>> security/selinux/ss/services.c | 62
> >>> ++++++++++++++++++++++++++++++
> >>> 9 files changed, 180 insertions(+)
> >>>
> >>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> >>> index 080f34e..9cac282 100644
> >>> --- a/include/linux/lsm_hooks.h
> >>> +++ b/include/linux/lsm_hooks.h
> >>> @@ -1336,6 +1336,20 @@
> >>> * @inode we wish to get the security context of.
> >>> * @ctx is a pointer in which to place the allocated
> >>> security context.
> >>> * @ctxlen points to the place to put the length of @ctx.
> >>> + *
> >>> + * Security hooks for policy brief
> >>> + *
> >>> + * @policy_brief:
> >>> + *
> >>> + * Returns a string containing a brief info of the
> >>> policydb, in the
> >>> + * following form:
> >>> + * <0 or 1 for enforce>:<0 or 1 for
> >>> checkreqprot>:<hashalg>=<checksum>
> >> This sure looks like SELinux specific information. If the Spiffy
> >> security module has multiple values for enforcement (e.g. off, soft
> >> and hard) this interface definition does not work. What is a
> >> "checkreqprot", and what is it for?
> >>
> >> I expect that you have no interest (or incentive) in supporting
> >> security modules other than SELinux, and that's OK. What's I'm after
> >> is an interface that another security module could use if someone
> >> where interested (or inspired) to do so.
> >>
> >> Rather than a string with predefined positional values (something I
> >> was taught not to do when 1 MIPS and 1 MEG was a big computer) you
> >> might use "enforce=<value>:checkreqprot=<value>:hashalg=<checksum>"
> > No objection to the above, although it makes his updating code for
> > enforce/checkreqprot a bit uglier.
>
> Sure, but can you imagine trying to use find(1) if the options where positional?
>
>
> >> for SELinux and define @policy_brief as
> >>
> >> A string containing colon separated name and value pairs
> >> that will be parsed and interpreted by the security module
> >> or modules.
> > Actually, I'm not clear it will be parsed or interpreted by the
> > security module(s). I think he is just fetching it and then doing a
> > simple comparison to check for inconsistencies between clients and the
> > server, and optionally admins/users can read it and interpret it as
> > they see fit.
>
> OK, in which case human eyes *need* the name as well as the value.
> That, and strcmp(value, "enforce=0") is no harder than strcmp(value, "0").
>
> >> You already have it right for the "hashalg" field. If you want to be
> >> really forward looking you could use names field names that identify
> >> the security module that uses them, such as
> >>
> >> "selinux/enforce=1:selinux/checkreqprot=0:selinux/MD5=8675309"
> > That seems a bit verbose, particularly the duplicated selinux/ bit.
>
> True that, on the other hand
>
> "selinux(enforce=1:checkreqprot=0:MD5=8675309)"
>
> would be harder to parse. Either works for me.
>
> >> Note that I put "selinux/" onto the MD5 as well. You may have
> >> multiple modules that use this interface on a system at the same time
> >> in the not to distant future:
> >>
> >> selinux/enforce=1:selinux/checkreqprot=0:
> >> selinux/MD5=8675309:spiffy/enforce=soft:
> >> spiffy/updatefreq=32544:spiffy/SHA256=84521
> >>
> >> If you deal with this now it won't be a major headache to deal with
> >> later.
> >>
> >>> + *
> >>> + * @brief: pointer to buffer holding brief
> >>> + * @len: in: brief buffer length if no alloc, out: brief
> >>> string len
> >>> + * @alloc: whether to allocate buffer for brief or not
> >>> + * On success 0 is returned , or negative value on error.
> >>> + *
> >>> * This is the main security structure.
> >>> */
> >>>
> >>> @@ -1568,6 +1582,7 @@
> >>> int (*inode_setsecctx)(struct dentry *dentry, void *ctx,
> >>> u32 ctxlen);
> >>> int (*inode_getsecctx)(struct inode *inode, void **ctx,
> >>> u32 *ctxlen);
> >>>
> >>> + int (*policy_brief)(char **brief, size_t *len, bool
> >>> alloc);
> >>> #ifdef CONFIG_SECURITY_NETWORK
> >>> int (*unix_stream_connect)(struct sock *sock, struct sock *other,
> >>> struct sock *newsk);
> >>> @@ -1813,6 +1828,7 @@ struct security_hook_heads {
> >>> struct list_head inode_notifysecctx;
> >>> struct list_head inode_setsecctx;
> >>> struct list_head inode_getsecctx;
> >>> + struct list_head policy_brief;
> >>> #ifdef CONFIG_SECURITY_NETWORK
> >>> struct list_head unix_stream_connect;
> >>> struct list_head unix_may_send;
> >>> diff --git a/include/linux/security.h b/include/linux/security.h
> >>> index af675b5..3b72053 100644
> >>> --- a/include/linux/security.h
> >>> +++ b/include/linux/security.h
> >>> @@ -377,6 +377,8 @@ int security_sem_semop(struct sem_array *sma,
> >>> struct sembuf *sops, int security_inode_notifysecctx(struct inode
> >>> *inode, void *ctx,
> >>> u32 ctxlen);
> >>> int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32
> >>> ctxlen); int security_inode_getsecctx(struct inode *inode, void
> >>> **ctx, u32 *ctxlen);
> >>> +
> >>> +int security_policy_brief(char **brief, size_t *len, bool alloc);
> >>> #else /* CONFIG_SECURITY */
> >>> struct security_mnt_opts {
> >>> };
> >>> @@ -1166,6 +1168,11 @@ static inline int
> >>> security_inode_getsecctx(struct inode *inode, void **ctx, u32 {
> >>> return -EOPNOTSUPP;
> >>> }
> >>> +
> >>> +static inline int security_policy_brief(char **brief, size_t *len,
> >>> bool alloc)
> >>> +{
> >>> + return -EOPNOTSUPP;
> >>> +}
> >>> #endif /* CONFIG_SECURITY */
> >>>
> >>> #ifdef CONFIG_SECURITY_NETWORK
> >>> diff --git a/security/security.c b/security/security.c index
> >>> b9fea39..954b391 100644
> >>> --- a/security/security.c
> >>> +++ b/security/security.c
> >>> @@ -1285,6 +1285,12 @@ int security_inode_getsecctx(struct inode
> >>> *inode, void **ctx, u32 *ctxlen) }
> >>> EXPORT_SYMBOL(security_inode_getsecctx);
> >>>
> >>> +int security_policy_brief(char **brief, size_t *len, bool alloc) {
> >>> + return call_int_hook(policy_brief, -EOPNOTSUPP, brief,
> >>> len, alloc);
> >>> +}
> >>> +EXPORT_SYMBOL(security_policy_brief);
> >>> +
> >>> #ifdef CONFIG_SECURITY_NETWORK
> >>>
> >>> int security_unix_stream_connect(struct sock *sock, struct sock
> >>> *other, struct sock *newsk) diff --git a/security/selinux/hooks.c
> >>> b/security/selinux/hooks.c index e67a526..da245e8 100644
> >>> --- a/security/selinux/hooks.c
> >>> +++ b/security/selinux/hooks.c
> >>> @@ -6063,6 +6063,11 @@ static int selinux_inode_getsecctx(struct
> >>> inode *inode, void **ctx, u32 *ctxlen)
> >>> *ctxlen = len;
> >>> return 0;
> >>> }
> >>> +
> >>> +static int selinux_policy_brief(char **brief, size_t *len, bool
> >>> alloc)
> >>> +{
> >>> + return security_policydb_brief(brief, len, alloc); }
> >>> #ifdef CONFIG_KEYS
> >>>
> >>> static int selinux_key_alloc(struct key *k, const struct cred
> >>> *cred, @@ -6277,6 +6282,8 @@ static int
> >>> selinux_key_getsecurity(struct key *key, char **_buffer)
> >>> LSM_HOOK_INIT(inode_setsecctx, selinux_inode_setsecctx),
> >>> LSM_HOOK_INIT(inode_getsecctx, selinux_inode_getsecctx),
> >>>
> >>> + LSM_HOOK_INIT(policy_brief, selinux_policy_brief),
> >>> +
> >>> LSM_HOOK_INIT(unix_stream_connect,
> >>> selinux_socket_unix_stream_connect),
> >>> LSM_HOOK_INIT(unix_may_send,
> >>> selinux_socket_unix_may_send),
> >>>
> >>> diff --git a/security/selinux/include/security.h
> >>> b/security/selinux/include/security.h
> >>> index f979c35..a0d4d7d 100644
> >>> --- a/security/selinux/include/security.h
> >>> +++ b/security/selinux/include/security.h
> >>> @@ -97,6 +97,8 @@ enum {
> >>> int security_load_policy(void *data, size_t len); int
> >>> security_read_policy(void **data, size_t *len); size_t
> >>> security_policydb_len(void);
> >>> +int security_policydb_brief(char **brief, size_t *len, bool
> >>> alloc);
> >>> +void security_policydb_update_info(u32 requested);
> >>>
> >>> int security_policycap_supported(unsigned int req_cap);
> >>>
> >>> diff --git a/security/selinux/selinuxfs.c
> >>> b/security/selinux/selinuxfs.c index 50062e7..8c9f5b7 100644
> >>> --- a/security/selinux/selinuxfs.c
> >>> +++ b/security/selinux/selinuxfs.c
> >>> @@ -159,6 +159,7 @@ static ssize_t sel_write_enforce(struct file
> >>> *file, const char __user *buf,
> >>> from_kuid(&init_user_ns,
> >>> audit_get_loginuid(current)),
> >>> audit_get_sessionid(current));
> >>> selinux_enforcing = new_value;
> >>> + security_policydb_update_info(SECURITY__SETENFORCE
> >>> );
> >>> if (selinux_enforcing)
> >>> avc_ss_reset(0);
> >>> selnl_notify_setenforce(selinux_enforcing);
> >>> @@ -621,6 +622,7 @@ static ssize_t sel_write_checkreqprot(struct
> >>> file *file, const char __user *buf,
> >>> goto out;
> >>>
> >>> selinux_checkreqprot = new_value ? 1 : 0;
> >>> + security_policydb_update_info(SECURITY__SETCHECKREQPROT);
> >>> length = count;
> >>> out:
> >>> kfree(page);
> >>> diff --git a/security/selinux/ss/policydb.c
> >>> b/security/selinux/ss/policydb.c index 0080122..58e73f5 100644
> >>> --- a/security/selinux/ss/policydb.c
> >>> +++ b/security/selinux/ss/policydb.c
> >>> @@ -32,11 +32,13 @@
> >>> #include <linux/errno.h>
> >>> #include <linux/audit.h>
> >>> #include <linux/flex_array.h>
> >>> +#include <crypto/hash.h>
> >>> #include "security.h"
> >>>
> >>> #include "policydb.h"
> >>> #include "conditional.h"
> >>> #include "mls.h"
> >>> +#include "objsec.h"
> >>> #include "services.h"
> >>>
> >>> #define _DEBUG_HASHES
> >>> @@ -879,6 +881,8 @@ void policydb_destroy(struct policydb *p)
> >>> ebitmap_destroy(&p->filename_trans_ttypes);
> >>> ebitmap_destroy(&p->policycaps);
> >>> ebitmap_destroy(&p->permissive_map);
> >>> +
> >>> + kfree(p->policybrief);
> >>> }
> >>>
> >>> /*
> >>> @@ -2220,6 +2224,73 @@ static int ocontext_read(struct policydb *p,
> >>> struct policydb_compat_info *info, }
> >>>
> >>> /*
> >>> + * Compute summary of a policy database binary representation
> >>> file,
> >>> + * and store it into a policy database structure.
> >>> + */
> >>> +static int policydb_brief(struct policydb *policydb, void *ptr) {
> >>> + struct policy_file *fp = ptr;
> >>> + struct crypto_shash *tfm;
> >>> + char hashalg[] = "sha256";
> >>> + size_t hashsize;
> >>> + u8 *hashval;
> >>> + int idx;
> >>> + unsigned char *p;
> >>> +
> >>> + if (policydb->policybrief)
> >>> + return -EINVAL;
> >>> +
> >>> + tfm = crypto_alloc_shash(hashalg, 0, 0);
> >>> + if (IS_ERR(tfm)) {
> >>> + printk(KERN_ERR "Failed to alloc crypto hash
> >>> %s\n", hashalg);
> >>> + return PTR_ERR(tfm);
> >>> + }
> >>> +
> >>> + hashsize = crypto_shash_digestsize(tfm);
> >>> + hashval = kmalloc(hashsize, GFP_KERNEL);
> >>> + if (hashval == NULL) {
> >>> + crypto_free_shash(tfm);
> >>> + return -ENOMEM;
> >>> + }
> >>> +
> >>> + {
> >>> + int rc;
> >>> +
> >>> + SHASH_DESC_ON_STACK(desc, tfm);
> >>> + desc->tfm = tfm;
> >>> + desc->flags = 0;
> >>> + rc = crypto_shash_digest(desc, fp->data, fp->len,
> >>> hashval);
> >>> + crypto_free_shash(tfm);
> >>> + if (rc) {
> >>> + printk(KERN_ERR "Failed
> >>> crypto_shash_digest: %d\n", rc);
> >>> + kfree(hashval);
> >>> + return rc;
> >>> + }
> >>> + }
> >>> +
> >>> + /* policy brief is in the form:
> >>> + * <0 or 1 for enforce>:<0 or 1 for
> >>> checkreqprot>:<hashalg>=<checksum>
> >>> + */
> >>> + policydb->policybrief = kzalloc(5 + strlen(hashalg) +
> >>> 2*hashsize + 1,
> >>> + GFP_KERNEL);
> >>> + if (policydb->policybrief == NULL) {
> >>> + kfree(hashval);
> >>> + return -ENOMEM;
> >>> + }
> >>> +
> >>> + sprintf(policydb->policybrief, "%d:%d:%s=",
> >>> + selinux_enforcing, selinux_checkreqprot, hashalg);
> >>> + p = policydb->policybrief + strlen(policydb->policybrief);
> >>> + for (idx = 0; idx < hashsize; idx++) {
> >>> + snprintf(p, 3, "%02x", hashval[idx]);
> >>> + p += 2;
> >>> + }
> >>> + kfree(hashval);
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +/*
> >>> * Read the configuration data from a policy database binary
> >>> * representation file into a policy database structure.
> >>> */
> >>> @@ -2238,6 +2309,11 @@ int policydb_read(struct policydb *p, void
> >>> *fp)
> >>> if (rc)
> >>> return rc;
> >>>
> >>> + /* Compute summary of policy, and store it in policydb */
> >>> + rc = policydb_brief(p, fp);
> >>> + if (rc)
> >>> + goto bad;
> >>> +
> >>> /* Read the magic number and string length. */
> >>> rc = next_entry(buf, fp, sizeof(u32) * 2);
> >>> if (rc)
> >>> diff --git a/security/selinux/ss/policydb.h
> >>> b/security/selinux/ss/policydb.h index 725d594..31689d2f 100644
> >>> --- a/security/selinux/ss/policydb.h
> >>> +++ b/security/selinux/ss/policydb.h
> >>> @@ -293,6 +293,8 @@ struct policydb {
> >>> size_t len;
> >>>
> >>> unsigned int policyvers;
> >>> + /* summary computed on the policy */
> >>> + unsigned char *policybrief;
> >>>
> >>> unsigned int reject_unknown : 1;
> >>> unsigned int allow_unknown : 1;
> >>> diff --git a/security/selinux/ss/services.c
> >>> b/security/selinux/ss/services.c index 60d9b02..3bbe649 100644
> >>> --- a/security/selinux/ss/services.c
> >>> +++ b/security/selinux/ss/services.c
> >>> @@ -2170,6 +2170,68 @@ size_t security_policydb_len(void) }
> >>>
> >>> /**
> >>> + * security_policydb_brief - Get policydb brief
> >>> + * @brief: pointer to buffer holding brief
> >>> + * @len: in: brief buffer length if no alloc, out: brief string
> >>> len
> >>> + * @alloc: whether to allocate buffer for brief or not
> >>> + *
> >>> + * On success 0 is returned , or negative value on error.
> >>> + **/
> >>> +int security_policydb_brief(char **brief, size_t *len, bool alloc)
> >>> +{
> >>> + size_t policybrief_len;
> >>> +
> >>> + if (!ss_initialized || brief == NULL)
> >>> + return -EINVAL;
> >>> +
> >>> + read_lock(&policy_rwlock);
> >>> + policybrief_len = strlen(policydb.policybrief);
> >>> + read_unlock(&policy_rwlock);
> >>> +
> >>> + if (alloc)
> >>> + /* *brief must be kfreed by caller in this case */
> >>> + *brief = kzalloc(policybrief_len + 1, GFP_KERNEL);
> >>> + else
> >>> + /*
> >>> + * if !alloc, caller must pass a buffer that
> >>> + * can hold policybrief_len+1 chars
> >>> + */
> >>> + if (*len < policybrief_len + 1) {
Kind of a weird way to do else if...
> >>> + /* put in *len the string size we need to
> >>> write */
> >>> + *len = policybrief_len;
> >>> + return -ENAMETOOLONG;
> >>> + }
> >>> +
> >>> + if (*brief == NULL)
> >>> + return -ENOMEM;
> >>> +
> >>> + read_lock(&policy_rwlock);
> >>> + *len = strlen(policydb.policybrief);
Isn't this: policybrief_len from above? No need to recompute.
> >>> + strncpy(*brief, policydb.policybrief, *len);
> >>> + read_unlock(&policy_rwlock);
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +void security_policydb_update_info(u32 requested) {
> >>> + /* policy brief is in the form:
> >>> + * <0 or 1 for enforce>:<0 or 1 for
> >>> checkreqprot>:<hashalg>=<checksum>
> >>> + */
> >>> +
> >>> + if (!ss_initialized)
> >>> + return;
> >>> +
> >>> + /* update global policydb, needs write lock */
> >>> + write_lock_irq(&policy_rwlock);
> >>> + if (requested == SECURITY__SETENFORCE)
> >>> + policydb.policybrief[0] = '0' + selinux_enforcing;
> >>> + else if (requested == SECURITY__SETCHECKREQPROT)
> >>> + policydb.policybrief[2] = '0' +
> >>> selinux_checkreqprot;
> >>> + write_unlock_irq(&policy_rwlock);
> >>> +}
> >>> +
> >>> +/**
> >>> * security_port_sid - Obtain the SID for a port.
> >>> * @protocol: protocol number
> >>> * @port: port number
>
> --
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