On Fri, 2017-05-05 at 19:10 +0900, 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.
>
> Signed-off-by: Sebastien Buisson <sbuisson@xxxxxxx>
> ---
> include/linux/lsm_hooks.h | 2 +
> include/linux/security.h | 7 ++++
> security/security.c | 6 +++
> security/selinux/hooks.c | 11 +++++-
> security/selinux/include/security.h | 2 +
> security/selinux/selinuxfs.c | 6 ++-
> security/selinux/ss/policydb.c | 70
> +++++++++++++++++++++++++++++++++++
> security/selinux/ss/policydb.h | 3 ++
> security/selinux/ss/services.c | 73
> +++++++++++++++++++++++++++++++++++++
> 9 files changed, 178 insertions(+), 2 deletions(-)
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index e67a526..b4dd605 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -104,8 +104,10 @@
> static int __init enforcing_setup(char *str)
> {
> unsigned long enforcing;
> - if (!kstrtoul(str, 0, &enforcing))
> + if (!kstrtoul(str, 0, &enforcing)) {
> selinux_enforcing = enforcing ? 1 : 0;
> + security_policydb_update_info(NULL);
I don't think you need this. You are unlikely to request the policy
brief until after policy has been loaded (and if you do, you'll only
get a partial result), so you can just defer setting up the enforcing
field until the initial policy load, and then update it on subsequent
writes to /sys/fs/selinux/enforce.
> + }
> return 1;
> }
> __setup("enforcing=", enforcing_setup);
> diff --git a/security/selinux/selinuxfs.c
> b/security/selinux/selinuxfs.c
> index ce71718..b959ee7 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -55,8 +55,10 @@
> static int __init checkreqprot_setup(char *str)
> {
> unsigned long checkreqprot;
> - if (!kstrtoul(str, 0, &checkreqprot))
> + if (!kstrtoul(str, 0, &checkreqprot)) {
> selinux_checkreqprot = checkreqprot ? 1 : 0;
> + security_policydb_update_info(NULL);
> + }
Ditto. Just initialize it with the rest of the info on initial policy
load, and update it on writes to checkreqprot.
> return 1;
> }
> __setup("checkreqprot=", checkreqprot_setup);
> diff --git a/security/selinux/ss/policydb.c
> b/security/selinux/ss/policydb.c
> index 0080122..9eb2f82 100644
> --- a/security/selinux/ss/policydb.c
> +++ b/security/selinux/ss/policydb.c
> @@ -32,6 +32,8 @@
> #include <linux/errno.h>
> #include <linux/audit.h>
> #include <linux/flex_array.h>
> +#include <crypto/hash.h>
> +#include <crypto/sha.h>
> #include "security.h"
>
> #include "policydb.h"
> @@ -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 +2224,67 @@ 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";
> + int hashsize = SHA256_DIGEST_SIZE;
size_t
> + char hashval[hashsize];
unsigned char or u8
> + 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);
> + }
Should you be checking crypto_shash_digestsize(tfm) against sizeof
hashval, or allocating hashval based on it instead? Not a problem now,
but if you ever change the algorithm and forget to update the
hashsize...
> +
> + {
> + int rc;
> +
> + SHASH_DESC_ON_STACK(desc, tfm);
> + desc->tfm = tfm;
> + desc->flags = 0;
> + rc = crypto_shash_init(desc);
> + if (rc) {
> + printk(KERN_ERR "Failed to init shash\n");
> + crypto_free_shash(tfm);
> + return rc;
> + }
> +
> + crypto_shash_update(desc, fp->data, fp->len);
> + crypto_shash_final(desc, hashval);
Just use crypto_shash_digest(); handles _init, _update, and _final for
you in one call.
> + crypto_free_shash(tfm);
> + }
> +
> + /* 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)
> + return -ENOMEM;
> +
> + sprintf(policydb->policybrief, "x:x:%s=", hashalg);
Couldn't you just directly set the enforcing and checkreqprot fields
above? No need to call another function.
> + security_policydb_update_info(policydb);
> + p = policydb->policybrief + strlen(policydb->policybrief);
> + for (idx = 0; idx < hashsize; idx++) {
> + snprintf(p, 3, "%02x", (unsigned
> char)(hashval[idx]));
No need to cast if you fix the type above.
> + p += 2;
> + }
> + policydb->policybrief_len = (size_t)(p - policydb-
> >policybrief);
This length is actually computable at build time, right? It isn't
variant based on policy, just on hash algorithm. No need to store it
in the policydb.
> +
> + return 0;
> +}
> +
> +/*
> * Read the configuration data from a policy database binary
> * representation file into a policy database structure.
> */
> @@ -2238,6 +2303,11 @@ int policydb_read(struct policydb *p, void
> *fp)
> if (rc)
> return rc;
>
> + /* Compute sumarry of policy, and store it in policydb */
summary
> + 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/services.c
> b/security/selinux/ss/services.c
> index 60d9b02..9a94f8e 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2170,6 +2170,79 @@ 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)
> +{
> + int rc = 0;
> + size_t policybrief_len;
> +
> + if (brief == NULL)
> + return -EINVAL;
You can return immediately if !ss_initialized.
> +
> + read_lock(&policy_rwlock);
> + policybrief_len = policydb.policybrief_len;
The length is fixed by the hash algorithm. No need to fetch it.
> + if (policydb.policybrief == NULL)
> + rc = -EAGAIN;
This shouldn't ever be possible if ss_initialized, right?
> + read_unlock(&policy_rwlock);
> +
> + if (rc)
> + return rc;
> +
> + 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) {
> + /* put in *len the string size we need to
> write */
> + *len = policybrief_len;
> + return -ENAMETOOLONG;
> + }
> +
> + if (*brief == NULL)
> + return -ENOMEM;
> +
> + read_lock(&policy_rwlock);
> + strncpy(*brief, policydb.policybrief,
> policydb.policybrief_len);
> + *len = policydb.policybrief_len;
> + read_unlock(&policy_rwlock);
> +
> + return rc;
> +}
> +
> +void security_policydb_update_info(void *p)
> +{
> + /* policy brief is in the form:
> + * <0 or 1 for enforce>:<0 or 1 for
> checkreqprot>:<hashalg>=<checksum>
> + */
if (!ss_initialized)
return;
> + if (p) {
> + struct policydb *poldb = p;
> + /* update policydb given as parameter if possible */
> + if (poldb->policybrief) {
> + poldb->policybrief[0] = '0' +
> selinux_enforcing;
> + poldb->policybrief[2] = '0' +
> selinux_checkreqprot;
This case could be handled directly in the caller.
> + }
> + } else {
> + /* update global policydb, needs write lock */
> + write_lock_irq(&policy_rwlock);
> + if (policydb.policybrief) {
Don't need this once ss_initialized is set.
> + policydb.policybrief[0] = '0' +
> selinux_enforcing;
> + policydb.policybrief[2] = '0' +
> selinux_checkreqprot;
> + }
Technically only need to update one of the two fields at any given
time, and the caller can specify which one. But maybe it isn't worth
it.
> + write_unlock_irq(&policy_rwlock);
> + }
> +}
> +
> +/**
> * security_port_sid - Obtain the SID for a port.
> * @protocol: protocol number
> * @port: port number
