Re: [PATCH] lsm: cleanup repeated lsm_blob_size_update() calls in lsm_prepare()

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

On Jun 29, 2026 Matt Bobrowski <mattbobrowski@google.com> wrote:
> 
> Centralize the definition of LSM security blob fields using an X-macro
> (LSM_BLOBS_LIST). This reduces repetitive boilerplate code across
> struct lsm_blob_sizes, blob size registration in lsm_prepare(), and
> debug log printing in security_init().
> 
> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
> ---
>  include/linux/lsm_hooks.h | 42 ++++++++++++++++------------
>  security/lsm_init.c       | 59 ++++++++++-----------------------------
>  2 files changed, 38 insertions(+), 63 deletions(-)
> 
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index b4f8cad53ddb..0e73b22bdeea 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -98,28 +98,34 @@ struct security_hook_list {
>  	const struct lsm_id *lsmid;
>  } __randomize_layout;
>  
> +#define LSM_BLOBS_LIST(X) \
> +	X(cred)          \
> +	X(file)          \
> +	X(backing_file)  \
> +	X(ib)            \
> +	X(inode)         \
> +	X(sock)          \
> +	X(superblock)    \
> +	X(ipc)           \
> +	X(key)           \
> +	X(msg_msg)       \
> +	X(perf_event)    \
> +	X(task)          \
> +	X(tun_dev)       \
> +	X(xattr_count)   \
> +	X(bdev)          \
> +	X(bpf_map)       \
> +	X(bpf_prog)      \
> +	X(bpf_token)
> +
>  /*
>   * Security blob size or offset data.
> + * Note: lbs_xattr_count is the number of xattr slots in new_xattrs array.
>   */
>  struct lsm_blob_sizes {
> -	unsigned int lbs_cred;
> -	unsigned int lbs_file;
> -	unsigned int lbs_backing_file;
> -	unsigned int lbs_ib;
> -	unsigned int lbs_inode;
> -	unsigned int lbs_sock;
> -	unsigned int lbs_superblock;
> -	unsigned int lbs_ipc;
> -	unsigned int lbs_key;
> -	unsigned int lbs_msg_msg;
> -	unsigned int lbs_perf_event;
> -	unsigned int lbs_task;
> -	unsigned int lbs_xattr_count; /* num xattr slots in new_xattrs array */
> -	unsigned int lbs_tun_dev;
> -	unsigned int lbs_bdev;
> -	unsigned int lbs_bpf_map;
> -	unsigned int lbs_bpf_prog;
> -	unsigned int lbs_bpf_token;
> +#define LSM_BLOB_SIZE(name) unsigned int lbs_##name;
> +	LSM_BLOBS_LIST(LSM_BLOB_SIZE);
> +#undef LSM_BLOB_SIZE
>  };

Generally speaking I greatly prefer to see the structure fields typed out
as it makes it easier to find them using grep, code indexers, etc.  There
is a similar argument for the security_init() changes (below).

> diff --git a/security/lsm_init.c b/security/lsm_init.c
> index 7c0fd17f1601..c256f1c33efa 100644
> --- a/security/lsm_init.c
> +++ b/security/lsm_init.c
> @@ -282,40 +282,24 @@ static void __init lsm_blob_size_update(unsigned int *sz_req,
>   * lsm_prepare - Prepare the LSM framework for a new LSM
>   * @lsm: LSM definition
>   */
> -static void __init lsm_prepare(struct lsm_info *lsm)
> +static void __init lsm_prepare(const struct lsm_info *lsm)
>  {
>  	struct lsm_blob_sizes *blobs = lsm->blobs;
>  
>  	if (!blobs)
>  		return;
>  
> -	/* Register the LSM blob sizes. */
> -	blobs = lsm->blobs;
> -	lsm_blob_size_update(&blobs->lbs_cred, &blob_sizes.lbs_cred);
> -	lsm_blob_size_update(&blobs->lbs_file, &blob_sizes.lbs_file);
> -	lsm_blob_size_update(&blobs->lbs_backing_file,
> -			     &blob_sizes.lbs_backing_file);
> -	lsm_blob_size_update(&blobs->lbs_ib, &blob_sizes.lbs_ib);
> -	/* inode blob gets an rcu_head in addition to LSM blobs. */
> +	/* The inode blob (inode->i_security) gets an rcu_head in addition to
> +	 * LSM blobs.
> +	 */
>  	if (blobs->lbs_inode && blob_sizes.lbs_inode == 0)
>  		blob_sizes.lbs_inode = sizeof(struct rcu_head);
> -	lsm_blob_size_update(&blobs->lbs_inode, &blob_sizes.lbs_inode);
> -	lsm_blob_size_update(&blobs->lbs_ipc, &blob_sizes.lbs_ipc);
> -	lsm_blob_size_update(&blobs->lbs_key, &blob_sizes.lbs_key);
> -	lsm_blob_size_update(&blobs->lbs_msg_msg, &blob_sizes.lbs_msg_msg);
> -	lsm_blob_size_update(&blobs->lbs_perf_event,
> -			     &blob_sizes.lbs_perf_event);
> -	lsm_blob_size_update(&blobs->lbs_sock, &blob_sizes.lbs_sock);
> -	lsm_blob_size_update(&blobs->lbs_superblock,
> -			     &blob_sizes.lbs_superblock);
> -	lsm_blob_size_update(&blobs->lbs_task, &blob_sizes.lbs_task);
> -	lsm_blob_size_update(&blobs->lbs_tun_dev, &blob_sizes.lbs_tun_dev);
> -	lsm_blob_size_update(&blobs->lbs_xattr_count,
> -			     &blob_sizes.lbs_xattr_count);
> -	lsm_blob_size_update(&blobs->lbs_bdev, &blob_sizes.lbs_bdev);
> -	lsm_blob_size_update(&blobs->lbs_bpf_map, &blob_sizes.lbs_bpf_map);
> -	lsm_blob_size_update(&blobs->lbs_bpf_prog, &blob_sizes.lbs_bpf_prog);
> -	lsm_blob_size_update(&blobs->lbs_bpf_token, &blob_sizes.lbs_bpf_token);
> +
> +	/* Register the LSM blob sizes. */
> +#define UPDATE_LSM_BLOB_SIZE(name) \
> +	lsm_blob_size_update(&blobs->lbs_##name, &blob_sizes.lbs_##name);
> +	LSM_BLOBS_LIST(UPDATE_LSM_BLOB_SIZE);
> +#undef UPDATE_LSM_BLOB_SIZE
>  }

This is one case where the macro approach *might* have some value, but as
it is the one instance, and multiple sequential blob operations like this
are going to be *very* limited, I'm not sure there is enough value to
be worth the change.

I appreciate the initiative to search out areas that you think could use
improvement, but for the reasons mentioned, I'm not going to merge this
patch.

> @@ -441,25 +425,10 @@ int __init security_init(void)
>  		lsm_prepare(*lsm);
>  
>  	if (lsm_debug) {
> -		lsm_pr("blob(cred) size %d\n", blob_sizes.lbs_cred);
> -		lsm_pr("blob(file) size %d\n", blob_sizes.lbs_file);
> -		lsm_pr("blob(backing_file) size %d\n",
> -		       blob_sizes.lbs_backing_file);
> -		lsm_pr("blob(ib) size %d\n", blob_sizes.lbs_ib);
> -		lsm_pr("blob(inode) size %d\n", blob_sizes.lbs_inode);
> -		lsm_pr("blob(ipc) size %d\n", blob_sizes.lbs_ipc);
> -		lsm_pr("blob(key) size %d\n", blob_sizes.lbs_key);
> -		lsm_pr("blob(msg_msg)_size %d\n", blob_sizes.lbs_msg_msg);
> -		lsm_pr("blob(sock) size %d\n", blob_sizes.lbs_sock);
> -		lsm_pr("blob(superblock) size %d\n", blob_sizes.lbs_superblock);
> -		lsm_pr("blob(perf_event) size %d\n", blob_sizes.lbs_perf_event);
> -		lsm_pr("blob(task) size %d\n", blob_sizes.lbs_task);
> -		lsm_pr("blob(tun_dev) size %d\n", blob_sizes.lbs_tun_dev);
> -		lsm_pr("blob(xattr) count %d\n", blob_sizes.lbs_xattr_count);
> -		lsm_pr("blob(bdev) size %d\n", blob_sizes.lbs_bdev);
> -		lsm_pr("blob(bpf_map) size %d\n", blob_sizes.lbs_bpf_map);
> -		lsm_pr("blob(bpf_prog) size %d\n", blob_sizes.lbs_bpf_prog);
> -		lsm_pr("blob(bpf_token) size %d\n", blob_sizes.lbs_bpf_token);
> +#define PRINT_LSM_BLOB_SIZE(name) \
> +	lsm_pr("blob(" #name ") size %d\n", blob_sizes.lbs_##name);
> +		LSM_BLOBS_LIST(PRINT_LSM_BLOB_SIZE);
> +#undef PRINT_LSM_BLOB_SIZE

This is another case where having the text string grep'able can be a good
thing.

--
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