On Tue, Apr 9, 2019 at 5:42 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> ---
> 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.
> +
> + return size;
> + }
>
> hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
> if (lsm != NULL && strcmp(lsm, hp->lsm))
> continue;
> + if (lsm == NULL && loh->lsm && strcmp(loh->lsm, hp->lsm))
> + continue;
> return hp->hook.setprocattr(name, value, size);
> }
> return -EINVAL;
> --
> 2.19.1
>
