Re: [PATCH v9 10/11] SELinux: Add selfattr hooks

Kees Cook
2023-04-21T19:58:04Z

On Fri, Apr 21, 2023 at 10:42:58AM -0700, Casey Schaufler wrote:
> Add hooks for setselfattr and getselfattr. These hooks are not very
> different from their setprocattr and getprocattr equivalents, and
> much of the code is shared.
>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Cc: selinux@vger.kernel.org
> Cc: Paul Moore <paul@paul-moore.com>
> ---
> security/selinux/hooks.c | 153 +++++++++++++++++++++++++++++++--------
> 1 file changed, 123 insertions(+), 30 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 9403aee75981..9bc6206fb1ef 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -6348,8 +6348,8 @@ static void selinux_d_instantiate(struct dentry *dentry, struct inode *inode)
> inode_doinit_with_dentry(inode, dentry);
> }
>
> -static int selinux_getprocattr(struct task_struct *p,
> - const char *name, char **value)
> +static int selinux_lsm_getattr(unsigned int attr, struct task_struct *p,
> + char **value)
> {
> const struct task_security_struct *__tsec;
> u32 sid;
> @@ -6367,20 +6367,27 @@ static int selinux_getprocattr(struct task_struct *p,
> goto bad;
> }
>
> - if (!strcmp(name, "current"))
> + switch (attr) {
> + case LSM_ATTR_CURRENT:
> sid = __tsec->sid;
> - else if (!strcmp(name, "prev"))
> + break;
> + case LSM_ATTR_PREV:
> sid = __tsec->osid;
> - else if (!strcmp(name, "exec"))
> + break;
> + case LSM_ATTR_EXEC:
> sid = __tsec->exec_sid;
> - else if (!strcmp(name, "fscreate"))
> + break;
> + case LSM_ATTR_FSCREATE:
> sid = __tsec->create_sid;
> - else if (!strcmp(name, "keycreate"))
> + break;
> + case LSM_ATTR_KEYCREATE:
> sid = __tsec->keycreate_sid;
> - else if (!strcmp(name, "sockcreate"))
> + break;
> + case LSM_ATTR_SOCKCREATE:
> sid = __tsec->sockcreate_sid;
> - else {
> - error = -EINVAL;
> + break;
> + default:
> + error = -EOPNOTSUPP;
> goto bad;
> }
> rcu_read_unlock();
> @@ -6398,7 +6405,7 @@ static int selinux_getprocattr(struct task_struct *p,
> return error;
> }
>
> -static int selinux_setprocattr(const char *name, void *value, size_t size)
> +static int selinux_lsm_setattr(u64 attr, void *value, size_t size)
> {
> struct task_security_struct *tsec;
> struct cred *new;
> @@ -6409,28 +6416,36 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
> /*
> * Basic control over ability to set these attributes at all.
> */
> - if (!strcmp(name, "exec"))
> + switch (attr) {
> + case LSM_ATTR_CURRENT:
> + error = avc_has_perm(&selinux_state,
> + mysid, mysid, SECCLASS_PROCESS,
> + PROCESS__SETCURRENT, NULL);
> + break;
> + case LSM_ATTR_EXEC:
> error = avc_has_perm(&selinux_state,
> mysid, mysid, SECCLASS_PROCESS,
> PROCESS__SETEXEC, NULL);
> - else if (!strcmp(name, "fscreate"))
> + break;
> + case LSM_ATTR_FSCREATE:
> error = avc_has_perm(&selinux_state,
> mysid, mysid, SECCLASS_PROCESS,
> PROCESS__SETFSCREATE, NULL);
> - else if (!strcmp(name, "keycreate"))
> + break;
> + case LSM_ATTR_KEYCREATE:
> error = avc_has_perm(&selinux_state,
> mysid, mysid, SECCLASS_PROCESS,
> PROCESS__SETKEYCREATE, NULL);
> - else if (!strcmp(name, "sockcreate"))
> + break;
> + case LSM_ATTR_SOCKCREATE:
> error = avc_has_perm(&selinux_state,
> mysid, mysid, SECCLASS_PROCESS,
> PROCESS__SETSOCKCREATE, NULL);
> - else if (!strcmp(name, "current"))
> - error = avc_has_perm(&selinux_state,
> - mysid, mysid, SECCLASS_PROCESS,
> - PROCESS__SETCURRENT, NULL);
> - else
> - error = -EINVAL;
> + break;
> + default:
> + error = -EOPNOTSUPP;
> + break;
> + }
> if (error)
> return error;
>
> @@ -6442,13 +6457,14 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
> }
> error = security_context_to_sid(&selinux_state, value, size,
> &sid, GFP_KERNEL);
> - if (error == -EINVAL && !strcmp(name, "fscreate")) {
> + if (error == -EINVAL && attr == LSM_ATTR_FSCREATE) {
> if (!has_cap_mac_admin(true)) {
> struct audit_buffer *ab;
> size_t audit_size;
>
> - /* We strip a nul only if it is at the end, otherwise the
> - * context contains a nul and we should audit that */
> + /* We strip a nul only if it is at the end,
> + * otherwise the context contains a nul and
> + * we should audit that */
> if (str[size - 1] == '\0')
> audit_size = size - 1;
> else
> @@ -6459,7 +6475,8 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
> if (!ab)
> return error;
> audit_log_format(ab, "op=fscreate invalid_context=");
> - audit_log_n_untrustedstring(ab, value, audit_size);
> + audit_log_n_untrustedstring(ab, value,
> + audit_size);
> audit_log_end(ab);
>
> return error;
> @@ -6483,11 +6500,11 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
> checks and may_create for the file creation checks. The
> operation will then fail if the context is not permitted. */
> tsec = selinux_cred(new);
> - if (!strcmp(name, "exec")) {
> + if (attr == LSM_ATTR_EXEC) {
> tsec->exec_sid = sid;
> - } else if (!strcmp(name, "fscreate")) {
> + } else if (attr == LSM_ATTR_FSCREATE) {
> tsec->create_sid = sid;
> - } else if (!strcmp(name, "keycreate")) {
> + } else if (attr == LSM_ATTR_KEYCREATE) {
> if (sid) {
> error = avc_has_perm(&selinux_state, mysid, sid,
> SECCLASS_KEY, KEY__CREATE, NULL);
> @@ -6495,9 +6512,9 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
> goto abort_change;
> }
> tsec->keycreate_sid = sid;
> - } else if (!strcmp(name, "sockcreate")) {
> + } else if (attr == LSM_ATTR_SOCKCREATE) {
> tsec->sockcreate_sid = sid;
> - } else if (!strcmp(name, "current")) {
> + } else if (attr == LSM_ATTR_CURRENT) {
> error = -EINVAL;
> if (sid == 0)
> goto abort_change;
> @@ -6542,6 +6559,80 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
> return error;
> }
>
> +static int selinux_getselfattr(unsigned int __user attr,
> + struct lsm_ctx __user *ctx, size_t *size,
> + u32 __user flags)
> +{
> + char *value;
> + size_t total_len;
> + int len;
> + int rc = 1;
> +
> + len = selinux_lsm_getattr(attr, current, &value);
> + if (len < 0)
> + return len;
> +
> + total_len = ALIGN(len + sizeof(*ctx), 8);

struct_size(ctx, ctx, len)

> +
> + if (total_len > *size)
> + rc = -E2BIG;
> + else
> + lsm_fill_user_ctx(ctx, value, len, LSM_ID_SELINUX, 0);
> +
> + *size = total_len;
> + return rc;
> +}
> +
> +static int selinux_setselfattr(unsigned int __user attr,
> + struct lsm_ctx __user *ctx, size_t __user size,
> + u32 __user flags)
> +{
> + struct lsm_ctx *lctx;
> + void *context;
> + int rc;
> +
> + context = kmalloc(size, GFP_KERNEL);
> + if (context == NULL)
> + return -ENOMEM;
> +
> + lctx = (struct lsm_ctx *)context;
> + if (copy_from_user(context, ctx, size))
> + rc = -EFAULT;
> + else if (lctx->ctx_len > size)
> + rc = -EINVAL;
> + else
> + rc = selinux_lsm_setattr(attr, lctx + 1, lctx->ctx_len);

Same nits as before:
- "context" isn't needed
- lctx + 1 doesn't exist: lctx->ctx does
- "u32 __user" isn't a sane type

> +
> + kfree(context);
> + if (rc > 0)
> + return 0;
> + return rc;
> +}
> +
> +static int selinux_getprocattr(struct task_struct *p,
> + const char *name, char **value)
> +{
> + unsigned int attr = lsm_name_to_attr(name);
> + int rc;
> +
> + if (attr) {
> + rc = selinux_lsm_getattr(attr, p, value);
> + if (rc != -EOPNOTSUPP)
> + return rc;
> + }
> +
> + return -EINVAL;
> +}
> +
> +static int selinux_setprocattr(const char *name, void *value, size_t size)
> +{
> + int attr = lsm_name_to_attr(name);
> +
> + if (attr)
> + return selinux_lsm_setattr(attr, value, size);
> + return -EINVAL;
> +}
> +
> static int selinux_ismaclabel(const char *name)
> {
> return (strcmp(name, XATTR_SELINUX_SUFFIX) == 0);
> @@ -7183,6 +7274,8 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>
> LSM_HOOK_INIT(d_instantiate, selinux_d_instantiate),
>
> + LSM_HOOK_INIT(getselfattr, selinux_getselfattr),
> + LSM_HOOK_INIT(setselfattr, selinux_setselfattr),
> LSM_HOOK_INIT(getprocattr, selinux_getprocattr),
> LSM_HOOK_INIT(setprocattr, selinux_setprocattr),
>
> --
> 2.39.2
>

--
Kees Cook