Re: [PATCH v6 1/2] selinux: add brief info to policydb

[William Roberts]

On Wed, May 17, 2017 at 11:30 AM, Stephen Smalley <sds@xxxxxxxxxxxxx> wrote:
> On Thu, 2017-05-18 at 02:09 +0900, Sebastien Buisson wrote:
>> Add policybrief field to struct policydb. It holds a brief info
>> of the policydb, made of colon separated name and value pairs
>> that give information about how the policy is applied in the
>> security module(s).
>> Note that the ordering of the fields in the string may change.
>>
>> 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. It is useful for any network or
>> distributed file system that cares about how SELinux is enforced
>> on its client nodes. This information is used to detect changes
>> to the policy on file system client nodes, and can be forwarded
>> to file system server nodes. Depending on how the policy is
>> enforced on client side, server can refuse connection.
>>
>> Signed-off-by: Sebastien Buisson <sbuisson@xxxxxxx>
>
> Looks good to me, but we need to see the patch that uses the LSM hook
> interface too.  Also, I would split up this patch and fold your second
> patch into one of the parts.  You could have a first patch that
> implements the support within SELinux and uses it from selinuxfs (no
> dependency on the LSM hook interface or the SELinux hook function), a
> second patch that adds the LSM hook interface and SELinux hook function
> to expose it outside of SELinux, and then a third patch to call the
> hook from lustre.

The more I keep looking at this the more I dislike the interface.
We're actually building an interface that defeats any LSM abstraction,
and clients of the interface have to poll and parse to find out if
something they care about changed.

I think the interface should be inverted and provide an interface
to register callbacks so clients can just set a callback and be
notified of a changes.


>
>> ---
>>  include/linux/lsm_hooks.h           | 20 +++++++++
>>  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      | 88
>> +++++++++++++++++++++++++++++++++++++
>>  security/selinux/ss/policydb.h      |  3 ++
>>  security/selinux/ss/services.c      | 67
>> ++++++++++++++++++++++++++++
>>  9 files changed, 202 insertions(+)
>>
>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
>> index 080f34e..0bc0260 100644
>> --- a/include/linux/lsm_hooks.h
>> +++ b/include/linux/lsm_hooks.h
>> @@ -1336,6 +1336,24 @@
>>   *   @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.
>> The string
>> + *   contains colon separated name and value pairs that give
>> information
>> + *   about how the policy is applied in the security module(s).
>> + *   Note that the ordering of the fields in the string may
>> change.
>> + *
>> + *   @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
>> + *   If @alloc, *brief must be kfreed by caller.
>> + *   If not @alloc, caller must pass a buffer that can hold
>> policy brief
>> + *   info (including terminating NUL).
>> + *   On success 0 is returned , or negative value on error.
>> + *
>>   * This is the main security structure.
>>   */
>>
>> @@ -1568,6 +1586,7 @@
>>       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 +1832,7 @@ 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 54b1e39..91247fc 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -1300,6 +1300,12 @@ 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 dddb81e..b6540f9 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -6071,6 +6071,11 @@ 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,
>> @@ -6285,6 +6290,8 @@ 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 ce71718..e8fe914 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 87d645d..b37b8e5 100644
>> --- a/security/selinux/ss/policydb.c
>> +++ b/security/selinux/ss/policydb.c
>> @@ -32,13 +32,20 @@
>>  #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"
>>
>> +static unsigned int policybrief_hash_size;
>> +static struct crypto_shash *policybrief_tfm;
>> +static const char policybrief_hash_alg[] = "sha256";
>> +unsigned int policybrief_len;
>> +
>>  #define _DEBUG_HASHES
>>
>>  #ifdef DEBUG_HASHES
>> @@ -874,6 +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);
>>  }
>>
>>  /*
>> @@ -2215,6 +2224,52 @@ 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)
>> +{
>> +     SHASH_DESC_ON_STACK(desc, policybrief_tfm);
>> +     struct policy_file *fp = ptr;
>> +     u8 *hashval;
>> +     int rc;
>> +
>> +     BUG_ON(policydb->policybrief);
>> +
>> +     hashval = kmalloc(policybrief_hash_size, GFP_KERNEL);
>> +     if (hashval == NULL)
>> +             return -ENOMEM;
>> +
>> +     desc->tfm = policybrief_tfm;
>> +     desc->flags = 0;
>> +     rc = crypto_shash_digest(desc, fp->data, fp->len, hashval);
>> +     if (rc) {
>> +             printk(KERN_ERR "Failed crypto_shash_digest: %d\n",
>> rc);
>> +             goto out_free;
>> +     }
>> +
>> +     /* policy brief is in the form:
>> +      * selinux(enforce=<0 or 1>:checkreqprot=<0 or
>> 1>:<hashalg>=<checksum>)
>> +      */
>> +     policydb->policybrief = kmalloc(policybrief_len,
>> GFP_KERNEL);
>> +     if (policydb->policybrief == NULL) {
>> +             rc = -ENOMEM;
>> +             goto out_free;
>> +     }
>> +     rc = snprintf(policydb->policybrief, policybrief_len,
>> +                   "selinux(enforce=%d:checkreqprot=%d:%s=%*phN)"
>> ,
>> +                   selinux_enforcing, selinux_checkreqprot,
>> +                   policybrief_hash_alg, policybrief_hash_size,
>> hashval);
>> +     BUG_ON(rc >= policybrief_len);
>> +     rc = 0;
>> +
>> +out_free:
>> +     kfree(hashval);
>> +
>> +     return rc;
>> +}
>> +
>> +/*
>>   * Read the configuration data from a policy database binary
>>   * representation file into a policy database structure.
>>   */
>> @@ -2233,6 +2288,11 @@ 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)
>> @@ -3451,3 +3511,31 @@ int policydb_write(struct policydb *p, void
>> *fp)
>>
>>       return 0;
>>  }
>> +
>> +static int __init init_policybrief_hash(void)
>> +{
>> +     struct crypto_shash *tfm;
>> +
>> +     if (!selinux_enabled)
>> +             return 0;
>> +
>> +     tfm = crypto_alloc_shash(policybrief_hash_alg, 0, 0);
>> +     if (IS_ERR(tfm)) {
>> +             printk(KERN_ERR "Failed to alloc crypto hash %s\n",
>> +                    policybrief_hash_alg);
>> +             return PTR_ERR(tfm);
>> +     }
>> +
>> +     policybrief_tfm = tfm;
>> +     policybrief_hash_size =
>> crypto_shash_digestsize(policybrief_tfm);
>> +
>> +     /* policy brief is in the form:
>> +      * selinux(enforce=<0 or 1>:checkreqprot=<0 or
>> 1>:<hashalg>=<checksum>)
>> +      */
>> +     policybrief_len = 35 + strlen(policybrief_hash_alg) +
>> +             2*policybrief_hash_size + 1;
>> +
>> +     return 0;
>> +}
>> +
>> +late_initcall(init_policybrief_hash);
>> diff --git a/security/selinux/ss/policydb.h
>> b/security/selinux/ss/policydb.h
>> index 725d594..2e5048c 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;
>> @@ -309,6 +311,7 @@ struct policydb {
>>  extern int policydb_role_isvalid(struct policydb *p, unsigned int
>> role);
>>  extern int policydb_read(struct policydb *p, void *fp);
>>  extern int policydb_write(struct policydb *p, void *fp);
>> +extern unsigned int policybrief_len;
>>
>>  #define PERM_SYMTAB_SIZE 32
>>
>> diff --git a/security/selinux/ss/services.c
>> b/security/selinux/ss/services.c
>> index 60d9b02..67eb80d 100644
>> --- a/security/selinux/ss/services.c
>> +++ b/security/selinux/ss/services.c
>> @@ -2170,6 +2170,73 @@ 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
>> + *
>> + * If @alloc, *brief must be kfreed by caller.
>> + * If not @alloc, caller must pass a buffer that can hold
>> policybrief_len
>> + * chars (including terminating NUL).
>> + * On success 0 is returned , or negative value on error.
>> + **/
>> +int security_policydb_brief(char **brief, size_t *len, bool alloc)
>> +{
>> +     if (!ss_initialized || brief == NULL)
>> +             return -EINVAL;
>> +
>> +     if (alloc) {
>> +             *brief = kzalloc(policybrief_len, GFP_KERNEL);
>> +     } else if (*len < policybrief_len) {
>> +             /* put in *len the string size we need to write */
>> +             *len = policybrief_len;
>> +             return -ENAMETOOLONG;
>> +     }
>> +
>> +     if (*brief == NULL)
>> +             return -ENOMEM;
>> +
>> +     read_lock(&policy_rwlock);
>> +     strcpy(*brief, policydb.policybrief);
>> +     /* *len is the length of the output string */
>> +     *len = policybrief_len - 1;
>> +     read_unlock(&policy_rwlock);
>> +
>> +     return 0;
>> +}
>> +
>> +void security_policydb_update_info(u32 requested)
>> +{
>> +     /* policy brief is in the form:
>> +      * selinux(enforce=<0 or 1>:checkreqprot=<0 or
>> 1>:<hashalg>=<checksum>)
>> +      */
>> +     char enforce[] = "enforce=";
>> +     char checkreqprot[] = "checkreqprot=";
>> +     char *p, *str;
>> +     int val;
>> +
>> +     if (!ss_initialized)
>> +             return;
>> +
>> +     if (requested == SECURITY__SETENFORCE) {
>> +             str = enforce;
>> +             val = selinux_enforcing;
>> +     } else if (requested == SECURITY__SETCHECKREQPROT) {
>> +             str = checkreqprot;
>> +             val = selinux_checkreqprot;
>> +     }
>> +
>> +     /* update global policydb, needs write lock */
>> +     write_lock_irq(&policy_rwlock);
>> +     p = strstr(policydb.policybrief, str);
>> +     if (p) {
>> +             p += strlen(str);
>> +             *p = '0' + val;
>> +     }
>> +     write_unlock_irq(&policy_rwlock);
>> +}
>> +
>> +/**
>>   * security_port_sid - Obtain the SID for a port.
>>   * @protocol: protocol number
>>   * @port: port number



-- 
Respectfully,

William C Roberts