Re: [PATCH v12 7/11] LSM: Helpers for attribute names and filling lsm_ctx

[Paul Moore <paul@paul-moore.com>]

On Jun 29, 2023 Casey Schaufler <casey@schaufler-ca.com> wrote:
> 
> Add lsm_name_to_attr(), which translates a text string to a
> LSM_ATTR value if one is available.
> 
> Add lsm_fill_user_ctx(), which fills a struct lsm_ctx, including
> the trailing attribute value.
> 
> All are used in module specific components of LSM system calls.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
> ---
>  include/linux/security.h | 14 +++++++++++++
>  security/lsm_syscalls.c  | 24 ++++++++++++++++++++++
>  security/security.c      | 44 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 82 insertions(+)

...

> diff --git a/security/security.c b/security/security.c
> index 199db23581f1..72ad7197b2c9 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -770,6 +770,50 @@ static int lsm_superblock_alloc(struct super_block *sb)
>  	return 0;
>  }
>  
> +/**
> + * lsm_fill_user_ctx - Fill a user space lsm_ctx structure
> + * @ctx: an LSM context to be filled
> + * @context: the new context value
> + * @context_size: the size of the new context value
> + * @id: LSM id
> + * @flags: LSM defined flags
> + *
> + * Fill all of the fields in a user space lsm_ctx structure.
> + * Caller is assumed to have verified that @ctx has enough space
> + * for @context.
> + *
> + * The total length is padded to a multiple of 64 bits to
> + * accomodate possible alignment issues.

We should drop the sentence above now that alignment is the caller's
responsibility, but since that was largely my fault I can fix this up
during the merge assuming you're okay with that Casey.

> + * Returns 0 on success, -EFAULT on a copyout error, -ENOMEM
> + * if memory can't be allocated.
> + */
> +int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
> +		      size_t context_size, u64 id, u64 flags)
> +{
> +	struct lsm_ctx *lctx;
> +	size_t locallen = struct_size(lctx, ctx, context_size);
> +	int rc = 0;
> +
> +	lctx = kzalloc(locallen, GFP_KERNEL);
> +	if (lctx == NULL)
> +		return -ENOMEM;
> +
> +	lctx->id = id;
> +	lctx->flags = flags;
> +	lctx->ctx_len = context_size;
> +	lctx->len = locallen;
> +
> +	memcpy(lctx->ctx, context, context_size);
> +
> +	if (copy_to_user(ctx, lctx, locallen))
> +		rc = -EFAULT;
> +
> +	kfree(lctx);
> +
> +	return rc;
> +}
> +
>  /*
>   * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
>   * can be accessed with:
> -- 
> 2.40.1

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