Re: [PATCH v13 10/11] SELinux: Add selfattr hooks

[Mickaël Salaün]

On Wed, Aug 02, 2023 at 10:44:33AM -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@xxxxxxxxxxxxxxxx>
> Cc: selinux@xxxxxxxxxxxxxxx
> Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
> ---
>  security/selinux/hooks.c | 136 +++++++++++++++++++++++++++++++--------
>  1 file changed, 109 insertions(+), 27 deletions(-)

> +static int selinux_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx,
> +			       size_t *size, u32 flags)
> +{
> +	char *value;
> +	size_t total_len;
> +	int len;
> +	int rc;
> +
> +	len = selinux_lsm_getattr(attr, current, &value);
> +	if (len < 0)
> +		return len;
> +
> +	total_len = ALIGN(struct_size(ctx, ctx, len), 8);
> +
> +	if (total_len > *size)

It looks a bit weird that size must be greater than all the LSM
attributes even when ctx is NULL. Same for other getselfattr hook
implementations.

> +		rc = -E2BIG;
> +	else if (ctx)
> +		rc = lsm_fill_user_ctx(ctx, value, len, LSM_ID_SELINUX, 0);
> +	else
> +		rc = 1;

Agreed with Paul, we should initialize rc to zero.

> +
> +	kfree(value);
> +	*size = total_len;
> +	if (rc < 0)
> +		return rc;
> +	return 1;
> +}
> +
> +static int selinux_setselfattr(unsigned int __user attr, struct lsm_ctx *ctx,
> +			       size_t __user size, u32 __user flags)

This __user attribute is dedicated to user pointers, not values.

> +{
> +	int rc;
> +

Good to see this refactoring!

> +	rc = selinux_lsm_setattr(attr, ctx->ctx, ctx->ctx_len);
> +	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);
> @@ -7080,6 +7160,8 @@ static struct security_hook_list selinux_hooks[] __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),
>  
> -- 
> 2.41.0
>