[PATCH 58/59] LSM: Specify which LSM to display with /proc/self/attr/display
Casey Schaufler
casey at schaufler-ca.com
Wed Apr 10 17:18:56 UTC 2019
On 4/10/2019 7:09 AM, Stephen Smalley wrote:
> On Wed, Apr 10, 2019 at 8:43 AM Stephen Smalley
> <stephen.smalley at gmail.com> wrote:
>> On Tue, Apr 9, 2019 at 5:42 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
>>> Create a new entry "display" in /proc/.../attr for controlling
>>> which LSM security information is displayed for a process.
>>> The name of an active LSM that supplies hooks for human readable
>>> data may be written to "display" to set the value. The name of
>>> the LSM currently in use can be read from "display".
>>>
>>> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
>>> ---
>>> fs/proc/base.c | 1 +
>>> security/security.c | 123 ++++++++++++++++++++++++++++++++++++++++++--
>>> 2 files changed, 121 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>>> index ddef482f1334..7bf70e041315 100644
>>> --- a/fs/proc/base.c
>>> +++ b/fs/proc/base.c
>>> @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = {
>>> ATTR(NULL, "fscreate", 0666),
>>> ATTR(NULL, "keycreate", 0666),
>>> ATTR(NULL, "sockcreate", 0666),
>>> + ATTR(NULL, "display", 0666),
>>> #ifdef CONFIG_SECURITY_SMACK
>>> DIR("smack", 0555,
>>> proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops),
>>> diff --git a/security/security.c b/security/security.c
>>> index 29149db3f78a..6e304aa796f9 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -47,9 +47,13 @@ static struct kmem_cache *lsm_inode_cache;
>>>
>>> char *lsm_names;
>>>
>>> -/* Socket blobs include infrastructure managed data */
>>> +/*
>>> + * Socket blobs include infrastructure managed data
>>> + * Cred blobs include context display instructions
>>> + */
>>> static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = {
>>> .lbs_sock = sizeof(struct lsm_export),
>>> + .lbs_cred = sizeof(struct lsm_one_hooks),
>>> };
>>>
>>> /**
>>> @@ -751,7 +755,10 @@ int lsm_superblock_alloc(struct super_block *sb)
>>>
>>> #define call_one_int_hook(FUNC, IRC, ...) ({ \
>>> int RC = IRC; \
>>> - if (lsm_base_one.FUNC.FUNC) \
>>> + struct lsm_one_hooks *LOH = current_cred()->security; \
>>> + if (LOH->FUNC.FUNC) \
>>> + RC = LOH->FUNC.FUNC(__VA_ARGS__); \
>>> + else if (LOH->lsm == NULL && lsm_base_one.FUNC.FUNC) \
>>> RC = lsm_base_one.FUNC.FUNC(__VA_ARGS__); \
>>> RC; \
>>> })
>>> @@ -1617,6 +1624,7 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
>>>
>>> void security_cred_free(struct cred *cred)
>>> {
>>> + struct lsm_one_hooks *loh;
>>> /*
>>> * There is a failure case in prepare_creds() that
>>> * may result in a call here with ->security being NULL.
>>> @@ -1626,26 +1634,44 @@ void security_cred_free(struct cred *cred)
>>>
>>> call_void_hook(cred_free, cred);
>>>
>>> + loh = cred->security;
>>> + kfree(loh->lsm);
>>> kfree(cred->security);
>>> cred->security = NULL;
>>> }
>>>
>>> +static int copy_loh(struct lsm_one_hooks *new, struct lsm_one_hooks *old,
>>> + gfp_t gfp)
>>> +{
>>> + *new = *old;
>>> + if (old->lsm) {
>>> + new->lsm = kstrdup(old->lsm, gfp);
>>> + if (unlikely(new->lsm == NULL))
>>> + return -ENOMEM;
>>> + }
>>> + return 0;
>>> +}
>>> +
>>> int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp)
>>> {
>>> int rc = lsm_cred_alloc(new, gfp);
>>>
>>> - if (rc)
>>> + if (unlikely(rc))
>>> return rc;
>>>
>>> rc = call_int_hook(cred_prepare, 0, new, old, gfp);
>>> if (unlikely(rc))
>>> security_cred_free(new);
>>> + else
>>> + rc = copy_loh(new->security, old->security, gfp);
>>> +
>>> return rc;
>>> }
>>>
>>> void security_transfer_creds(struct cred *new, const struct cred *old)
>>> {
>>> call_void_hook(cred_transfer, new, old);
>>> + WARN_ON(copy_loh(new->security, old->security, GFP_KERNEL));
>>> }
>>>
>>> void security_cred_getsecid(const struct cred *c, struct lsm_export *l)
>>> @@ -1960,10 +1986,28 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>>> char **value)
>>> {
>>> struct security_hook_list *hp;
>>> + struct lsm_one_hooks *loh = current_cred()->security;
>>> + char *s;
>>> +
>>> + if (!strcmp(name, "display")) {
>>> + if (loh->lsm)
>>> + s = loh->lsm;
>>> + else if (lsm_base_one.lsm)
>>> + s = lsm_base_one.lsm;
>>> + else
>>> + return -EINVAL;
>>> +
>>> + *value = kstrdup(s, GFP_KERNEL);
>>> + if (*value)
>>> + return strlen(s);
>>> + return -ENOMEM;
>>> + }
>>>
>>> hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
>>> if (lsm != NULL && strcmp(lsm, hp->lsm))
>>> continue;
>>> + if (lsm == NULL && loh->lsm && strcmp(loh->lsm, hp->lsm))
>>> + continue;
>>> return hp->hook.getprocattr(p, name, value);
>>> }
>>> return -EINVAL;
>>> @@ -1973,10 +2017,83 @@ int security_setprocattr(const char *lsm, const char *name, void *value,
>>> size_t size)
>>> {
>>> struct security_hook_list *hp;
>>> + struct lsm_one_hooks *loh = current_cred()->security;
>>> + bool found = false;
>>> + char *s;
>>> +
>>> + /*
>>> + * End the passed name at a newline.
>>> + */
>>> + s = strnchr(value, size, '\n');
>>> + if (s)
>>> + *s = '\0';
>>> +
>>> + if (!strcmp(name, "display")) {
>>> + union security_list_options secid_to_secctx;
>>> + union security_list_options secctx_to_secid;
>>> + union security_list_options socket_getpeersec_stream;
>>> +
>>> + if (size == 0 || size >= 100)
>>> + return -EINVAL;
>>> +
>>> + secid_to_secctx.secid_to_secctx = NULL;
>>> + hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx,
>>> + list) {
>>> + if (size >= strlen(hp->lsm) &&
>>> + !strncmp(value, hp->lsm, size)) {
>>> + secid_to_secctx = hp->hook;
>>> + found = true;
>>> + break;
>>> + }
>>> + }
>>> + secctx_to_secid.secctx_to_secid = NULL;
>>> + hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid,
>>> + list) {
>>> + if (size >= strlen(hp->lsm) &&
>>> + !strncmp(value, hp->lsm, size)) {
>>> + secctx_to_secid = hp->hook;
>>> + found = true;
>>> + break;
>>> + }
>>> + }
>>> + socket_getpeersec_stream.socket_getpeersec_stream = NULL;
>>> + hlist_for_each_entry(hp,
>>> + &security_hook_heads.socket_getpeersec_stream,
>>> + list) {
>>> + if (size >= strlen(hp->lsm) &&
>>> + !strncmp(value, hp->lsm, size)) {
>>> + socket_getpeersec_stream = hp->hook;
>>> + found = true;
>>> + break;
>>> + }
>>> + }
>>> + if (!found)
>>> + return -EINVAL;
>>> +
>>> + /*
>>> + * The named lsm is active and supplies one or more
>>> + * of the relevant hooks. Switch to it.
>>> + */
>>> + s = kmemdup(value, size + 1, GFP_KERNEL);
>>> + if (s == NULL)
>>> + return -ENOMEM;
>>> + s[size] = '\0';
>>> +
>>> + if (loh->lsm)
>>> + kfree(loh->lsm);
>>> + loh->lsm = s;
>>> + loh->secid_to_secctx = secid_to_secctx;
>>> + loh->secctx_to_secid = secctx_to_secid;
>>> + loh->socket_getpeersec_stream = socket_getpeersec_stream;
>> You can't just write to the cred security blob like this; it is a
>> shared data structure, not per-task.
> To be clear, you either need to perform a new = prepare_creds(); /*
> modify new->security as desired */; commit_creds(new); sequence here,
> or use the task security blob instead of the cred security blob. The
> latter seems more amenable to your needs.
You're right. The task blob makes more sense.
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